U.S. patent application number 16/905175 was filed with the patent office on 2021-12-23 for proppant coatings and methods of making.
This patent application is currently assigned to Saudi Arabian Oil Company. The applicant listed for this patent is Alfaisal University, Saudi Arabian Oil Company. Invention is credited to Edreese Alsharaeh, Mohan Raj Krishnan, Wengang Li.
Application Number | 20210395603 16/905175 |
Document ID | / |
Family ID | 1000004968181 |
Filed Date | 2021-12-23 |
United States Patent
Application |
20210395603 |
Kind Code |
A1 |
Li; Wengang ; et
al. |
December 23, 2021 |
PROPPANT COATINGS AND METHODS OF MAKING
Abstract
A coated proppant having a proppant particle, an intermediate
cross-linked terpolymer layer encapsulating the proppant particle,
and an outer resin layer encapsulating the intermediate
cross-linked terpolymer layer. The proppant particle is selected
from sand, ceramic, glass, and combinations thereof. The
intermediate cross-linked terpolymer layer includes styrene, methyl
methacrylate, and divinyl benzene. The outer resin layer includes a
cured epoxy resin formed from an epoxy resin and a curing
agent.
Inventors: |
Li; Wengang; (Dhahran,
SA) ; Alsharaeh; Edreese; (Riyadh, SA) ;
Krishnan; Mohan Raj; (Riyadh, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company
Alfaisal University |
Dhahran
Riyadh |
|
SA
SA |
|
|
Assignee: |
Saudi Arabian Oil Company
Dhahran
SA
Alfaisal University
Riyadh
SA
|
Family ID: |
1000004968181 |
Appl. No.: |
16/905175 |
Filed: |
June 18, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 8/805 20130101;
C08K 3/042 20170501; C08F 20/06 20130101; C08F 12/08 20130101; C08G
59/5033 20130101; C08K 5/03 20130101; C08G 59/5006 20130101 |
International
Class: |
C09K 8/80 20060101
C09K008/80; C08F 20/06 20060101 C08F020/06; C08G 59/50 20060101
C08G059/50; C08F 12/08 20060101 C08F012/08 |
Claims
1. A coated proppant comprising: a proppant particle; an
intermediate cross-linked terpolymer layer encapsulating the
proppant particle; and an outer resin layer encapsulating the
intermediate cross-linked terpolymer layer.
2. The coated proppant of claim 1, wherein the proppant particle is
selected from the group consisting of oxides, silicates, sand,
ceramic, resin, epoxy, plastic, mineral, glass, and combinations
thereof.
3. The coated proppant of claim 1, wherein the proppant particle is
selected from the group consisting of sand, ceramic, glass, and
combinations thereof.
4. The coated proppant of claim 1, wherein the intermediate
cross-linked terpolymer layer comprises a combination of monomers
and a cross-linking agent.
5. The coated proppant of claim 4, wherein the combination of
monomers comprises a first monomer and a second monomer that is
different from the first monomer.
6. The coated proppant of claim 5, wherein the first monomer is
cis- or trans-ethylene substituted aromatic organic compound and
the second monomer is an alkyl acrylate.
7. The coated proppant of claim 5, wherein the first monomer is
styrene.
8. The coated proppant of claim 5, wherein the second monomer is
methyl methacrylate.
9. The coated proppant of claim 5, wherein the first monomer is
styrene and the second monomer is methyl methacrylate.
10. The coated proppant of claim 5, wherein the first monomer is
present in the combination of monomers in an amount from 10.0 wt. %
to 90.0 wt. %, and the second monomer is present in the combination
of monomers in an amount from 10.0 wt. % to 90.0 wt. %.
11. The coated proppant of claim 10, wherein the first monomer is
present in the combination of monomers in an amount from 40.0 wt. %
to 60.0 wt. %, and the second monomer is present in the combination
of monomers in an amount from 40.0 wt. % to 60.0 wt. %.
12. The coated proppant of claim 4, wherein the cross-linking agent
is selected from the group consisting of divinyl benzene,
vinylpyridine, bis(vinylphenyl) ethane, bis(vinylbenzyloxy) hexane,
and combinations thereof.
13. The coated proppant of claim 12, wherein the cross-linking
agent comprises divinyl benzene.
14. The coated proppant of claim 4, wherein the cross-linking agent
is present as a super addition relative to the combination of
monomers in an amount from 0.5 wt. % to 30.0 wt. %.
15. The coated proppant of claim 4, wherein the cross-linking agent
is present as a super addition relative to the combination of
monomers in an amount from 1.0 wt. % to 15.0 wt. %.
16. The coated proppant of claim 1, wherein the outer resin layer
comprises a cured epoxy resin and graphene.
17. The coated proppant of claim 16, wherein the cured epoxy resin
is formed from an epoxy resin and a curing agent.
18. The coated proppant of claim 17, wherein the epoxy resin has
the following general formula: ##STR00007## wherein R and R' are
selected from the group consisting of a part of a six-membered
ring, a polyhydroxyphenol, a polybasic acid, a polyol, and
combinations thereof.
19. The coated proppant of claim 17, wherein the curing agent is
selected from the group consisting of aliphatic polyamines and
their derivatives, modified aliphatic amines, aromatic amines, and
combinations thereof.
20. The coated proppant of claim 1, wherein the coated proppant
produces fine production at a load of 12000 psi that is from 2.0%
to 10.0%.
21. The coated proppant of claim 1, wherein the coated proppant
produces fine production at a load of 10000 psi that is from 0.5%
to 5.0%.
22. The coated proppant of claim 1, wherein the coated proppant has
an elastic modulus from 4.0 GPa to 7.0 GPa.
23. The coated proppant of claim 1, wherein the coated proppant has
a hardness from 0.10 GPa to 0.40 GPa.
24. The coated proppant of claim 1, wherein the proppant particle
is selected from the group consisting of sand, ceramic, glass, and
combinations thereof; the intermediate cross-linked terpolymer
layer comprises styrene, methyl methacrylate, and divinyl benzene;
and the outer resin layer comprises a cured epoxy resin formed from
an epoxy resin and a curing agent, wherein the epoxy resin has the
following general formula: ##STR00008## wherein R and R' are
selected from the group consisting of a part of a six-membered
ring, a polyhydroxyphenol, a polybasic acid, a polyol, and
combinations thereof, and the curing agent is selected from the
group consisting of aliphatic polyamines and their derivatives,
modified aliphatic amines, aromatic amines, and combinations
thereof.
Description
TECHNICAL FIELD
[0001] Embodiments of the present disclosure generally relate to
proppant coatings, method of making the proppant coatings and
methods for using proppants having the proppant coating.
BACKGROUND
[0002] Hydraulic fracturing is a stimulation treatment routinely
performed on oil and gas wells. Hydraulic fracturing fluids are
pumped into the subsurface formation to be treated, causing
fractures to open in the subsurface formation. Proppants, such as
grains of sand of a particular size, may be mixed with the
treatment fluid to keep the fracture open when the treatment is
complete.
SUMMARY
[0003] It is often desirable during and after fracturing a
subsurface formation to hold the fractures open through the use of
proppants for more effective oil and gas production than without.
However, conventional uncoated proppants break under downhole
stress. Even coated proppants. Temperatures downhole exacerbate
this effect.
[0004] Proppant coatings are used to protect the proppant particle
from degradation by the presence of aqueous fluids at downhole
temperatures. The proppant coating increases the surface area of
the particle; therefore, the crush stress is distributed over a
larger area of the coated proppant particle. The proppant coating
also adheres to the proppant and prevents proppants that are
crushed from releasing proppant fines, which may migrate into the
formation and restrict flow conductivity of the formation.
Conventional proppant coating techniques to reduce both the crush
percentage and the generation of proppant fines are done at
temperatures greater than 250.degree. C. Conventional proppant
coatings are designed to cure completely prior to the use of coated
proppants in fracturing operations. However, even coated proppants
can break down when stresses are increased, such as at pressures
deep within a subsurface formation.
[0005] Accordingly, a need exists for proppant coatings, methods
for making proppant coatings, and methods of using coated proppants
downhole that can withstand increased stresses. Coated proppants
often include a proppant coated with an intermediate polymer layer
and an outer resin layer. However, these structures may not be
strong enough to withstand pressures greater than 8000 pounds per
square inch (psi).
[0006] According to a first aspect, a coated proppant comprises: a
proppant particle; an intermediate cross-linked terpolymer layer
encapsulating the proppant particle; and an outer resin layer
encapsulating the intermediate cross-linked terpolymer layer.
[0007] A second aspect includes the coated proppant of the first
aspect, wherein the proppant particle is selected from the group
consisting of oxides, silicates, sand, ceramic, resin, epoxy,
plastic, mineral, glass, and combinations thereof.
[0008] A third aspect includes the coated proppant of the first or
second aspect, wherein the proppant particle is selected from the
group consisting of sand, ceramic, glass, and combinations
thereof.
[0009] A fourth aspect includes the coated proppant of any one of
the first to third aspects, wherein the intermediate cross-linked
terpolymer layer comprises a combination of monomers and a
cross-linking agent.
[0010] A fifth aspect includes the coated proppant of the fourth
aspect, wherein the combination of monomers comprises a first
monomer and a second monomer that is different from the first
monomer.
[0011] A sixth aspect includes the coated proppant of the fifth
aspect, wherein the first monomer is cis- or trans-ethylene
substituted aromatic organic compound and the second monomer is an
alkyl acrylate.
[0012] A seventh aspect includes the coated proppant of the fifth
or sixth aspects, wherein the first monomer is styrene.
[0013] An eighth aspect includes the coated proppant of any one of
the fifth to seventh aspects, wherein the second monomer is methyl
methacrylate.
[0014] A ninth aspect includes the coated proppant of any one of
the fifth to eighth aspects, wherein the first monomer is styrene
and the second monomer is methyl methacrylate.
[0015] A tenth aspect includes the coated proppant of any one of
the fifth to ninth aspects, wherein the first monomer is present in
the combination of monomers in an amount from 10.0 wt. % to 90.0
wt. %, and the second monomer is present in the combination of
monomers in an amount from 10.0 wt. % to 90.0 wt. %.
[0016] An eleventh aspect includes the coated proppant of any one
of the fifth to tenth aspects, wherein the wherein the first
monomer is present in the combination of monomers in an amount from
40.0 wt. % to 60.0 wt. %, and the second monomer is present in the
combination of monomers in an amount from 40.0 wt. % to 60.0 wt.
%.
[0017] A twelfth aspect includes the coated proppant of any one of
the fourth to eleventh aspects, wherein the cross-linking agent is
selected from the group consisting of divinyl benzene,
vinylpyridine, bis(vinylphenyl) ethane, bis(vinylbenzyloxy) hexane,
and combinations thereof.
[0018] A thirteenth aspect includes the coated proppant of any one
of the fourth to twelfth aspects, wherein the cross-linking agent
comprises divinyl benzene.
[0019] A fourteenth aspect includes the coated proppant of any one
of the fourth to thirteenth aspects, wherein the cross-linking
agent is present as a super addition relative to the combination of
monomers in an amount from 0.5 wt. % to 30.0 wt. %.
[0020] A fifteenth aspect includes the coated proppant of any one
of the fourth to fourteenth aspects, wherein the cross-linking
agent is present as a super addition relative to the combination of
monomers in an amount from 1.0 wt. % to 15.0 wt. %.
[0021] A sixteenth aspect includes the coated proppant of any one
of the first to fifteenth aspects, wherein the outer resin layer
comprises a cured epoxy resin and graphene.
[0022] A seventeenth aspect includes the coated proppant of the
sixteenth aspect, wherein the cured epoxy resin is formed from an
epoxy resin and a curing agent.
[0023] An eighteenth aspect includes the coated proppant of the
sixteenth or seventeenth aspects, wherein the epoxy resin has the
following general formula:
##STR00001##
wherein R and R' are selected from the group consisting of a part
of a six-membered ring, a polyhydroxyphenol, a polybasic acid, a
polyol, and combinations thereof.
[0024] A nineteenth aspect includes the coated proppant of the
seventeenth aspect, wherein the curing agent is selected from the
group consisting of aliphatic polyamines and their derivatives,
modified aliphatic amines, aromatic amines, and combinations
thereof.
[0025] A twentieth aspect includes the coated proppant of any one
of the first to nineteenth aspects, wherein the coated proppant
produces fine production at a load of 12000 psi that is from 2.0%
to 10.0%.
[0026] A twenty-first aspect includes the coated proppant of any
one of the first to twentieth aspects, wherein the coated proppant
produces fine production at a load of 10000 psi that is from 0.5%
to 5.0%.
[0027] A twenty-second aspect includes the coated proppant of any
one of the first to twenty-first aspects, wherein the coated
proppant has an elastic modulus from 4.0 GPa to 7.0 GPa.
[0028] A twenty-third aspect includes the coated proppant of any
one of the first to twenty-second aspects, wherein the coated
proppant has a hardness from 0.10 GPa to 0.40 GPa.
[0029] A twenty-fourth aspect includes the coated proppant of any
one of the first to twenty-third aspects, wherein the proppant
particle is selected from the group consisting of sand, ceramic,
glass, and combinations thereof; the intermediate cross-linked
terpolymer layer comprises styrene, methyl methacrylate, and
divinyl benzene; and the outer resin layer comprises a cured epoxy
resin formed from an epoxy resin and a curing agent, wherein the
epoxy resin has the following general formula:
##STR00002##
wherein R and R' are selected from the group consisting of a part
of a six-membered ring, a polyhydroxyphenol, a polybasic acid, a
polyol, and combinations thereof, and the curing agent is selected
from the group consisting of aliphatic polyamines and their
derivatives, modified aliphatic amines, aromatic amines, and
combinations thereof.
[0030] A twenty-fifth aspect included a method for producing a
coated proppant comprising an intermediate cross-linked terpolymer
layer, the method comprising: mixing a monomers solution comprising
a first monomer, a second monomer that is different from the first
monomer, a cross-linking agent, and an initiator; combining at
least one proppant particle with the monomers solution;
polymerizing the monomer solution on the surface of the at least
one proppant particle to form at least one proppant particle having
the intermediate cross-linked terpolymer layer on a surface of the
at least one proppant particle; mixing a resin solution comprising
an epoxy resin, a curing agent, and graphene; combining the at
least one proppant particle having the intermediate cross-linked
terpolymer layer on a surface of the at least one proppant particle
and the resin solution; curing the resin solution to form the
coated proppant comprising an intermediate cross-linked terpolymer
layer.
[0031] A twenty-sixth aspect includes the method of the
twenty-fifth aspect, wherein the proppant particle is selected from
the group consisting of sand, ceramic, glass, and combinations
thereof.
[0032] A twenty-seventh aspect includes the method of the
twenty-fifth or twenty-sixth aspect, wherein the first monomer is
cis- or trans-ethylene substituted aromatic organic compound and
the second monomer is an alkyl acrylate.
[0033] A twenty-eighth aspect includes the method of any one of the
twenty-fifth to twenty-seventh aspects, wherein the first monomer
is styrene and the second monomer is methyl methacrylate.
[0034] A twenty-ninth aspect includes the method of any one of the
twenty-fifth to twenty-eighth aspects, wherein the first monomer is
present in the combination of monomers in an amount from 10.0 wt. %
to 90.0 wt. %, and the second monomer is present in the combination
of monomers in an amount from 10.0 wt. % to 90.0 wt. %.
[0035] A thirtieth aspect includes the method of any one of the
twenty-fifth to twenty-ninth aspects, wherein the wherein the first
monomer is present in the combination of monomers in an amount from
40.0 wt. % to 60.0 wt. %, and the second monomer is present in the
combination of monomers in an amount from 40.0 wt. % to 60.0 wt.
%.
[0036] A thirty-first aspect includes the method of any one of the
twenty-fifth to thirtieth aspects, wherein the cross-linking agent
is selected from the group consisting of divinyl benzene,
vinylpyridine, bis(vinylphenyl) ethane, bis(vinylbenzyloxy) hexane,
and combinations thereof.
[0037] A thirty-second aspect includes the method of any one of the
twenty-fifth to thirty-first aspects, wherein the cross-linking
agent comprises divinyl benzene.
[0038] A thirty-third aspect includes the method of any one of the
twenty-fifth to thirty-second aspects, wherein the cross-linking
agent is present as a super addition relative to the first monomer
and the second monomer in an amount from 0.5 wt. % to 30.0 wt.
%.
[0039] A thirty-fourth aspect includes the method of any one of the
twenty-fifth to thirty-third aspects, wherein the cross-linking
agent is present as a super addition relative to the first monomer
and the second monomer in an amount from 1.0 wt. % to 15.0 wt.
%.
[0040] A thirty-fifth aspect includes the method of any one of the
twenty-fifth to thirty-fourth aspects, wherein the initiator is
selected from the group consisting of azoisobutyronitrile (AIBN),
benzoyl peroxide, tert-butyl peroxide, tert-butyl peracetate,
tert-butyl peroxybenzoate, tert-butyl hydroperoxide, peracetic
acid, potassium persulfate, and combinations thereof.
[0041] A thirty-sixth aspect includes the method of any one of the
twenty-fifth to thirty-fifth aspects, wherein the initiator is
present as a super addition relative to the first monomer and the
second monomer in an amount from 1.0 wt. % to 10.0 wt. %.
[0042] A thirty-seventh aspect includes the method of any one of
the twenty-fifth to thirty-sixth aspects, wherein the epoxy resin
has the following general formula:
##STR00003##
wherein R and R' are selected from the group consisting of a part
of a six-membered ring, a polyhydroxyphenol, a polybasic acid, a
polyol, and combinations thereof.
[0043] A thirty-eighth aspect includes the method of any one of the
twenty-fifth to thirty-seventh aspects, wherein the curing agent is
selected from the group consisting of aliphatic polyamines and
their derivatives, modified aliphatic amines, aromatic amines, and
combinations thereof.
[0044] A thirty-ninth aspect includes the method of any one of the
twenty-fifth to thirty-eighth aspects, wherein the epoxy resin is
present in a mixture of the epoxy resin and the curing agent in an
amount from 15.0 wt. % to 90.0 wt. %.
[0045] A fortieth aspect includes the method of any one of the
twenty-fifth to thirty-ninth aspects, wherein the epoxy resin is
present in a mixture of the epoxy resin and the curing agent in an
amount from 70.0 wt. % to 90.0 wt. %.
[0046] A forty-first aspect includes the method of any one of the
twenty-fifth to fortieth aspects, wherein the curing agent is
present in a mixture of the epoxy resin and the curing agent in an
amount from 10.0 wt. % to 85.0 wt. %.
[0047] A forty-second aspect includes the method of any one of the
twenty-fifth to forty-first aspects, wherein the curing agent is
present in a mixture of the epoxy resin and the curing agent in an
amount from 10.0 wt. % to 30.0 wt. %.
[0048] A forty-third aspect includes the method of any one of the
twenty-fifth to forty-second aspects, wherein the graphene is
present as a super addition relative to the epoxy resin and the
curing agent in an amount from 0.05 wt. % to 0.50 wt. %.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The following detailed description of specific embodiments
of the present disclosure can be best understood when read in
conjunction with the following drawing, where like structure is
indicated with like reference numerals and in which:
[0050] FIG. 1 is a schematic view of a proppant particle and a
coated proppant according to one or more embodiments described in
this disclosure;
[0051] FIG. 2 is schematic view of a cross-linking mechanism
according to one or more embodiments described in this
disclosure;
[0052] FIG. 3 graphically depicts the fine production of coated
proppants according to one or more embodiments described in this
disclosure and comparative proppants;
[0053] FIG. 4 graphically depicts the fine production of coated
proppants according to one or more embodiments described in this
disclosure;
[0054] FIG. 5 graphically depicts the glass transition temperatures
of coated proppants according to one or more embodiments described
in this disclosure and comparative proppants;
[0055] FIG. 6 graphically depicts the degradation temperatures of
coated proppants according to one or more embodiments described in
this disclosure and comparative proppants;
[0056] FIGS. 7A-7C are magnified images of coated proppants
according to one or more embodiments described in this disclosure
and comparative proppants; and
[0057] FIGS. 8A-8C are SEM images of coated proppants according to
one or more embodiments described in this disclosure and
comparative proppants.
DETAILED DESCRIPTION
[0058] As used throughout this disclosure, the term "polymer
backbone" or "copolymer backbone," which may also be called "the
main chain," is the linearly-oriented polymeric chain to which all
side chains or moieties are attached or grafted.
[0059] As used throughout this disclosure, the term "crosslinking"
refers to the covalent bonding of a first polymeric chain with a
second polymeric chain using a cross-linking agent.
[0060] As used throughout this disclosure, the term "hydraulic
fracturing" refers to a stimulation treatment performed on
reservoirs with a permeability of less than 10 milliDarcys.
Hydraulic fracturing fluids are pumped into a subsurface formation
such that fractures form. The wings of the fracture extend away
from the wellbore in opposing directions according to the natural
stresses within the subsurface formation. Proppants are mixed with
the treatment fluid to keep the fracture open when the treatment is
completed. Hydraulic fracturing creates fluid communication with a
subsurface formation and bypasses damage that may exist in the
near-wellbore area.
[0061] As used throughout this disclosure, the term "subsurface
formation" refers to a body of rock that is sufficiently
distinctive and continuous from the surrounding rock bodies that
the body of rock can be mapped as a distinct entity. A subsurface
formation is, therefore, sufficiently homogenous to form a single
identifiable unit containing similar rheological properties
throughout the subsurface formation, including, but not limited to,
porosity and permeability. A subsurface formation is the
fundamental unit of lithostratigraphy.
[0062] As used throughout this disclosure, the term "lithostatic
pressure" refers to the pressure of the weight of overburden, or
overlying rock, on a subsurface formation.
[0063] As used throughout this disclosure, the term "producing
subsurface formation" refers to the subsurface formation from which
hydrocarbons are produced.
[0064] As used throughout this disclosure, the term "proppants"
refers to particles capable to hold fractures open after a
hydraulic fracturing treatment is completed.
[0065] As used throughout this disclosure, the term "reservoir"
refers to a subsurface formation having sufficient porosity and
permeability to store and transmit fluids.
[0066] As used throughout this disclosure, the term "wellbore"
refers to the drilled hole or borehole, including the open hole or
uncased portion of the well. Borehole may refer to the void space
defined by the wellbore wall, where the rock face that bounds the
drilled hole defines the borehole.
[0067] The present disclosure is directed to compositions, methods
of production, and methods of using a proppant comprising a
cross-linked terpolymer intermediate coating and a resin outer
layer. In embodiments, and with reference to FIG. 1, the coated
proppant 100 comprises a proppant particle 110, an intermediate
cross-linked terpolymer layer 120 encapsulating the proppant
particle 110, and an outer resin layer 130 encapsulating the
intermediate cross-linked terpolymer layer 120. In the embodiment
shown in FIG. 1, the intermediate cross-linked terpolymer layer 120
directly encapsulates the proppant particle 110. As used herein
"directly encapsulates" means that a layer is in direct, physical
contact with the layer it encapsulates. Therefore, in the
embodiment shown in FIG. 1, the intermediate cross-linked
terpolymer layer 120 is in direct, physical contact with the
proppant particle 110. Similarly, in the embodiment shown in FIG.
1, the outer resin layer 130 directly encapsulates the intermediate
cross-linked terpolymer layer 120. In addition, in the embodiment
shown in FIG. 1, the outer resin layer 130 indirectly encapsulates
the proppant particle 110. As used herein, "indirectly
encapsulates" means that a layer is not in direct, physical contact
with the layer it is encapsulating, such as by the presence of an
intermediate layer. As used herein, "encapsulates,"
"encapsulation," "encapsulating," and the like without "directly"
or "indirectly" includes both direct and indirect
encapsulation.
[0068] In embodiments, the proppant particle 110 is directly
encapsulated by the intermediate cross-linked terpolymer layer 120,
and the intermediate cross-linked terpolymer layer 120 is directly
encapsulated by the outer resin layer 130. In embodiments, the
proppant particle is directly encapsulated by the intermediate
cross-linked terpolymer layer 120, and the intermediate
cross-linked terpolymer layer 120 is indirectly encapsulated by the
outer resin layer 130. In embodiments, the proppant particle is
indirectly encapsulated by the intermediate cross-linked terpolymer
layer 120, and the intermediate cross-linked terpolymer layer 120
is directly encapsulated by the outer resin layer 130. In
embodiments, the proppant particle is indirectly encapsulated by
the intermediate cross-linked terpolymer layer 120, and the
intermediate cross-linked terpolymer layer 120 is indirectly
encapsulated by the outer resin layer 130.
[0069] The proppant particle 110 may be chosen from any material
suitable for use in hydraulic fracturing applications. As
previously described, proppants are propping agent particles used
in hydraulic fracturing fluids to maintain and hold open subsurface
fractures during or following subsurface treatment. In some
embodiments, the proppant particle 110 may comprise particles of
materials such as oxides, silicates, sand, ceramic, resin, epoxy,
plastic, mineral, glass, or combinations thereof. For instance, the
proppant particle may comprise graded sand, treated sand, ceramic
proppant, plastic proppant, or other materials. The proppant
particle 110 may comprise particles of bauxite, sintered bauxite,
Ti4+/polymer composites, where the superscript "4+" stands for the
oxidation state of titanium, titanium nitride (TiN), or titanium
carbide. The proppant particle may comprise glass particles or
glass beads. Embodiments of the present disclosure may utilize at
least one proppant particle 110 and in embodiments in which more
than one proppant particle 110 is used, the proppant particles may
contain a mixture of two or more different materials or three or
more different materials.
[0070] The material of the proppant particle 110 may be chosen
based on the particular application and characteristics desired,
such as the depth of the subsurface formation in which the proppant
particles will be used, as proppant particles 110 with greater
mechanical strength are needed at greater lithostatic pressures.
For instance, ceramic proppant materials exhibit greater strength,
thermal resistance, and conductivity than sands. Additionally,
ceramic proppant materials have more uniform size and shape than
sands.
[0071] The proppant particle 110 may include various sizes or
shapes. In some embodiments, the one or more proppant particles 110
may have sizes from 8 mesh to 200 mesh (diameters from 74
micrometers (.mu.m) to 2.36 millimeters (mm)). In some embodiments,
the proppant particles 110 may have sizes from 8 mesh to 16 mesh
(diam. 2380 .mu.m to 1180 .mu.m), 16 mesh to 30 mesh (diam. 600
.mu.m to 1180 .mu.m), 20 mesh to 40 mesh (diam. 420 .mu.m to 840
.mu.m), 30 mesh to 50 mesh (diam. 300 .mu.m to 600 .mu.m), 40 mesh
to 70 mesh (diam. 212 .mu.m to 420 .mu.m) or 70 mesh to 140 mesh
(diam. 106 .mu.m to 212 .mu.m). The sphericity and roundness of the
proppant particles may also vary based on the desired
application.
[0072] In some embodiments, the proppant particles 110 may have a
rough surface texture that may increase adhesion of the
intermediate cross-linked terpolymer layer 120 coating to the
proppant particle 110. The proppant particles 110 surfaces may be
roughened to increase the surface area of the proppant particle 110
by any suitable physical or chemical method, including, for
example, using an appropriate etchant. In some embodiments, the
proppant particle 110 may have a surface that provides a desired
adhesion of the intermediate cross-linked terpolymer layer 120 to
the proppant particle 110 or may already be sufficiently rough
without a need for chemical or physical roughening. Specifically,
ball milling proppant particles 110 may provide relatively rounder
particles as well as particles with increased surface
roughness.
[0073] The term "rough" refers to a surface having at least one
deviation from the normalized plane of the surface, such as a
depression or protrusion. The surface may be uneven and irregular
and may have one or more imperfections, such as dimples, stipples,
bumps, or projections, or other surface defects. The rough surface
may have an arithmetic average roughness (Ra) of greater than or
equal to 1 nanometer (nm) (1 nm=0.001 .mu.m). Ra is defined as the
arithmetic average of the differences between the local surface
heights and the average surface height and can be described by
Equation 1, contemplating n measurements:
R a = 1 n .times. i = 1 n .times. y i Equation .times. .times. 1
##EQU00001##
[0074] In Equation 1, each yi is the amount of deviation from the
normalized plane of the surface (meaning the depth or height of a
depression or protrusion, respectively) of the absolute value of
the ith of n measurements. Thus, Ra is the arithmetic average of
the absolute values of n measurements of deviation y from the
normalized plane of the surface. In some embodiments, the surface
of the proppant particle 110 may have an Ra of greater than or
equal to 2 nm (0.002 .mu.m), or greater than or equal to 10 nm
(0.01 .mu.m), or greater than or equal to 50 nm (0.05 .mu.m), or
greater than or equal to 100 nm (0.1 .mu.m), or greater than or
equal to 1 .mu.m.
[0075] An intermediate cross-linked terpolymer layer 120 may,
according to embodiments, be formed directly or indirectly on
proppant particle 110. The following describes forming the
intermediate cross-linked terpolymer layer 120 directly to the
proppant particle 110 (thereby the intermediate cross-linked
terpolymer layer 120 directly encapsulates the proppant particle
110). However, it should be understood that according to
embodiments, the proppant particle 110 may be treated prior to
forming the intermediate cross-linked terpolymer layer 120 so that
the intermediate cross-linked terpolymer layer 120 indirectly
encapsulates the proppant particle 110. According to embodiments,
the intermediate cross-linked terpolymer layer 120 is formed to
have a three dimensional (3D) cross-linked polymer structure. This
may be accomplished by in situ bulk polymerization of a combination
of monomers and a cross-linking agent. According to embodiments, an
initiator is used to initiate the bulk polymerization of the
monomers and cross-linking agent.
[0076] According to one or more embodiments, the intermediate
cross-linked terpolymer layer 120 is formed on the proppant
particle 110 by combining proppant particles 110 with the
combination of monomers and the cross-linking agent. The initiator
may be coated onto the proppant particle 110 before the proppant
particle 110 is combined with the combination of monomers and the
cross-linking agent; the initiator may be added to a mixture of the
combination of monomers and the cross-linking agent; or the
initiator may be coated onto the proppant particle 110 before the
proppant particle 110 is combined with the combination of monomers
and cross-linking agent and the initiator is also added to a
mixture of the combination of monomers and the cross-linking
agent.
[0077] In embodiments, the combination of monomers may include cis-
or trans-ethylene substituted aromatic organic compound and an
alkyl acrylate. According to embodiments, the cis- or
trans-ethylene substituted aromatic organic compound is a styrene.
In embodiments, the styrene may be selected from the group
consisting of p-methyl styrene, p-floro styrene, p-chloro styrene
and p-bromo styrene, and combinations thereof. According to
embodiments, the alkyl acrylate is selected from the group
consisting of methyl acrylate, ethyl acrylate, methyl methacrylate,
ethyl methacrylate, methacrylic acid, butyl methacrylate,
hydroxyethyl methacrylate, and combinations thereof. In one or more
embodiments, the combination of monomers comprises styrene and
methyl methacrylate. The cross-linking agent is, according to one
or more embodiments, selected from the group consisting of divinyl
benzene, vinylpyridine, bis(vinylphenyl) ethane,
bis(vinylbenzyloxy) hexane, and combinations thereof. In one or
more embodiments, the cross-linking agent is divinyl benzene.
Although it should be understood that any of the above monomers and
cross-linking agents may be used in any combination, according to
embodiments, the proppant particles 110 are mixed with styrene and
methyl methacrylate--as the combination of monomers--and divinyl
benzene--as the cross-linking agent.
[0078] In one or more embodiments, the monomers may be mixed
together to form the combination of monomers before adding the
cross-linking agent. In embodiments, the combination of monomers
comprises a first monomer and a second monomer. The first monomer
is present in the combination of monomers in an amount from 10.0
wt. % to 90.0 wt. %, such as from 20.0 wt. % to 90.0 wt. %, from
30.0 wt. % to 90.0 wt. %, from 40.0 wt. % to 90.0 wt. %, from 50.0
wt. % to 90.0 wt. %, from 60.0 wt. % to 90.0 wt. %, from 70.0 wt. %
to 90.0 wt. %, or from 80.0 wt. % to 90.0 wt. %, from 10.0 wt. % to
80.0 wt. %, from 20.0 wt. % to 80.0 wt. %, from 30.0 wt. % to 80.0
wt. %, from 40.0 wt. % to 80.0 wt. %, from 50.0 wt. % to 80.0 wt.
%, from 60.0 wt. % to 80.0 wt. %, from 70.0 wt. % to 80.0 wt. %,
from 10.0 wt. % to 70.0 wt. %, from 20.0 wt. % to 70.0 wt. %, from
30.0 wt. % to 70.0 wt. %, from 40.0 wt. % to 70.0 wt. %, from 50.0
wt. % to 70.0 wt. %, from 60.0 wt. % to 70.0 wt. %, from 10.0 wt. %
to 60.0 wt. %, such as from 20.0 wt. % to 60.0 wt. %, from 30.0 wt.
% to 60.0 wt. %, from 40.0 wt. % to 60.0 wt. %, from 50.0 wt. % to
60.0 wt. %, from 10.0 wt. % to 50.0 wt. %, such as from 20.0 wt. %
to 50.0 wt. %, from 30.0 wt. % to 50.0 wt. %, from 40.0 wt. % to
50.0 wt. %, from 10.0 wt. % to 40.0 wt. %, from 20.0 wt. % to 40.0
wt. %, from 30.0 wt. % to 40.0 wt. %, from 10.0 wt. % to 30.0 wt.
%, from 20.0 wt. % to 30.0 wt. %, from 10.0 wt. % to 20.0 wt. %.
The second monomer is present in the combination of monomers in an
amount from 10.0 wt. % to 90.0 wt. %, such as from 20.0 wt. % to
90.0 wt. %, from 30.0 wt. % to 90.0 wt. %, from 40.0 wt. % to 90.0
wt. %, from 50.0 wt. % to 90.0 wt. %, from 60.0 wt. % to 90.0 wt.
%, from 70.0 wt. % to 90.0 wt. %, or from 80.0 wt. % to 90.0 wt. %,
from 10.0 wt. % to 80.0 wt. %, from 20.0 wt. % to 80.0 wt. %, from
30.0 wt. % to 80.0 wt. %, from 40.0 wt. % to 80.0 wt. %, from 50.0
wt. % to 80.0 wt. %, from 60.0 wt. % to 80.0 wt. %, from 70.0 wt. %
to 80.0 wt. %, from 10.0 wt. % to 70.0 wt. %, from 20.0 wt. % to
70.0 wt. %, from 30.0 wt. % to 70.0 wt. %, from 40.0 wt. % to 70.0
wt. %, from 50.0 wt. % to 70.0 wt. %, from 60.0 wt. % to 70.0 wt.
%, from 10.0 wt. % to 60.0 wt. %, such as from 20.0 wt. % to 60.0
wt. %, from 30.0 wt. % to 60.0 wt. %, from 40.0 wt. % to 60.0 wt.
%, from 50.0 wt. % to 60.0 wt. %, from 10.0 wt. % to 50.0 wt. %,
such as from 20.0 wt. % to 50.0 wt. %, from 30.0 wt. % to 50.0 wt.
%, from 40.0 wt. % to 50.0 wt. %, from 10.0 wt. % to 40.0 wt. %,
from 20.0 wt. % to 40.0 wt. %, from 30.0 wt. % to 40.0 wt. %, from
10.0 wt. % to 30.0 wt. %, from 20.0 wt. % to 30.0 wt. %, from 10.0
wt. % to 20.0 wt. %. According to one or more embodiments, the
first monomer is styrene and the second monomer is methyl
methacrylate. It should be understood that the monomers may be
mixed into the combination of monomers by any suitable, physical
mixing process, such as stirring, blending, agitating, sonicating,
and the like.
[0079] In embodiments, subsequent to mixing the combination of
monomer, a cross-linking agent is added to the combination of
monomers. The cross-linking agent is, according to embodiments,
added to the combination of monomers in amounts from 0.5 wt. % to
30.0 wt. %, such as 1.0 wt. % to 30.0 wt. %, from 2.5 wt. % to 30.0
wt. %, from 5.0 wt. % to 30.0 wt. %, from 7.5 wt. % to 30.0 wt. %,
from 10.0 wt. % to 30.0 wt. %, from 12.5 wt. % to 30.0 wt. %, from
15.0 wt. % to 30.0 wt. %, from 17.5 wt. % to 30.0 wt. %, from 20.0
wt. % to 30.0 wt. %, from 22.5 wt. % to 30.0 wt. %, from 25.0 wt. %
to 30.0 wt. %, from 27.5 wt. % to 30.0 wt. %, from 0.5 wt. % to
27.5 wt. %, 1.0 wt. % to 27.5 wt. %, from 2.5 wt. % to 27.5 wt. %,
from 5.0 wt. % to 27.5 wt. %, from 7.5 wt. % to 27.5 wt. %, from
10.0 wt. % to 27.5 wt. %, from 12.5 wt. % to 27.5 wt. %, from 15.0
wt. % to 27.5 wt. %, from 17.5 wt. % to 27.5 wt. %, from 20.0 wt. %
to 27.5 wt. %, from 22.5 wt. % to 27.5 wt. %, from 25.0 wt. % to
27.5 wt. %, from 0.5 wt. % to 25.0 wt. %, 1.0 wt. % to 25.0 wt. %,
from 2.5 wt. % to 25.0 wt. %, from 5.0 wt. % to 25.0 wt. %, from
7.5 wt. % to 25.0 wt. %, from 10.0 wt. % to 25.0 wt. %, from 12.5
wt. % to 25.0 wt. %, from 15.0 wt. % to 25.0 wt. %, from 17.5 wt. %
to 25.0 wt. %, from 20.0 wt. % to 25.0 wt. %, from 22.5 wt. % to
25.0 wt. %, from 0.5 wt. % to 22.5 wt. %, 1.0 wt. % to 22.5 wt. %,
from 2.5 wt. % to 22.5 wt. %, from 5.0 wt. % to 22.5 wt. %, from
7.5 wt. % to 22.5 wt. %, from 10.0 wt. % to 22.5 wt. %, from 12.5
wt. % to 22.5 wt. %, from 15.0 wt. % to 22.5 wt. %, from 17.5 wt. %
to 22.5 wt. %, from 20.0 wt. % to 22.5 wt. %, from 0.5 wt. % to
20.0 wt. %, 1.0 wt. % to 20.0 wt. %, from 2.5 wt. % to 20.0 wt. %,
from 5.0 wt. % to 20.0 wt. %, from 7.5 wt. % to 20.0 wt. %, from
10.0 wt. % to 20.0 wt. %, from 12.5 wt. % to 20.0 wt. %, from 15.0
wt. % to 20.0 wt. %, from 17.5 wt. % to 20.0 wt. %, from 0.5 wt. %
to 17.5 wt. %, 1.0 wt. % to 17.5 wt. %, from 2.5 wt. % to 17.5 wt.
%, from 5.0 wt. % to 17.5 wt. %, from 7.5 wt. % to 17.5 wt. %, from
10.0 wt. % to 17.5 wt. %, from 12.5 wt. % to 17.5 wt. %, from 15.0
wt. % to 17.5 wt. %, from 0.5 wt. % to 15.0 wt. %, 1.0 wt. % to
15.0 wt. %, from 2.5 wt. % to 15.0 wt. %, from 5.0 wt. % to 15.0
wt. %, from 7.5 wt. % to 15.0 wt. %, from 10.0 wt. % to 15.0 wt. %,
from 12.5 wt. % to 15.0 wt. %, from 0.5 wt. % to 12.5 wt. %, 1.0
wt. % to 12.5 wt. %, from 2.5 wt. % to 12.5 wt. %, from 5.0 wt. %
to 12.5 wt. %, from 7.5 wt. % to 12.5 wt. %, from 10.0 wt. % to
12.5 wt. %, from 0.5 wt. % to 10.0 wt. %, 1.0 wt. % to 10.0 wt. %,
from 2.5 wt. % to 10.0 wt. %, from 5.0 wt. % to 10.0 wt. %, from
7.5 wt. % to 10.0 wt. %, from 0.5 wt. % to 7.5 wt. %, 1.0 wt. % to
7.5 wt. %, from 2.5 wt. % to 7.5 wt. %, from 5.0 wt. % to 7.5 wt.
%, from 0.5 wt. % to 5.0 wt. %, 1.0 wt. % to 5.0 wt. %, from 2.5
wt. % to 5.0 wt. %, from 0.5 wt. % to 2.5 wt. %, 1.0 wt. % to 2.5
wt. %, or from 0.5 wt. % to 1.0 wt. %. The cross-linking agent is
added as a percentage of the combination of the monomers and the
cross-linking agent (e.g., if the combination of monomers weights
90 kg and 10 wt. % cross-linking agent is added, 10 kg of
cross-linking agent would be added to the 90 kg of the combination
of monomers). In embodiments, the cross-linking agent is divinyl
benzene. Without being bound by any particular theory, if too
little cross-linking agent is added, the cross-linked terpolymer
will likely not be properly formed, but if more than 30.0 wt. % of
the cross-linking agent is added, the intermediate cross-linked
terpolymer layer 120 will be composed of linear polymer chains and
the desired 3D structure will not be obtained. Accordingly, it is
believed that the desired 3D cross-linked polymer structure for the
intermediate cross-linked terpolymer layer 120 is achieved when the
cross-linking agent is added to the combination of monomers in
amounts from 0.5 wt. % to 30.0 wt. %.
[0080] As previously disclosed, an initiator may also be used to
aid the polymerization process. Initiators that may be used in
embodiments are selected from the group consisting of
azoisobutyronitrile (AIBN), benzoyl peroxide, tert-butyl peroxide,
tert-butyl peracetate, tert-butyl peroxybenzoate, tert-butyl
hydroperoxide, peracetic acid, potassium persulfate, and
combinations thereof. In embodiments, the initiator is AIBN. In
embodiments, the initiator is coated onto the proppant particle 110
before the proppant particle 110 is combined with either the
combination of monomers or the cross-linking agent. In some
embodiments, the initiator is added to the mixture of the combined
monomers and cross-linking agent. In some embodiments, the
initiator is coated onto the proppant particle before the proppant
particle 110 is combined with either the combination of monomers or
the cross-linking agent, and the initiator is also added to the
mixture of the combined monomers, and cross-linking agent.
[0081] According to one or more embodiments, the proppant particle
110 may be coated with the initiator by mixing the initiator with a
solvent and coating the proppant particle 110 with the mixture of
the initiator and the solvent. In embodiments, the solvent may be
selected from the group consisting of acetone, methanol, ethanol,
n-propanol, isopropanol, n-butanol, and combinations thereof. The
initiator is, according to embodiments, present in the mixture of
the initiator and the solvent in amounts from 1.0 wt. % to 10.0 wt.
%, such as from 2.0 wt. % to 10.0 wt. %, from 3.0 wt. % to 10.0 wt.
%, from 4.0 wt. % to 10.0 wt. %, from 5.0 wt. % to 10.0 wt. %, from
6.0 wt. % to 10.0 wt. %, from 7.0 wt. % to 10.0 wt. %, from 8.0 wt.
% to 10.0 wt. %, from 9.0 wt. % to 10.0 wt. %, from 1.0 wt. % to
9.0 wt. %, from 2.0 wt. % to 9.0 wt. %, from 3.0 wt. % to 9.0 wt.
%, from 4.0 wt. % to 9.0 wt. %, from 5.0 wt. % to 9.0 wt. %, from
6.0 wt. % to 9.0 wt. %, from 7.0 wt. % to 9.0 wt. %, from 8.0 wt. %
to 9.0 wt. %, from 1.0 wt. % to 8.0 wt. %, from 2.0 wt. % to 8.0
wt. %, from 3.0 wt. % to 8.0 wt. %, from 4.0 wt. % to 8.0 wt. %,
from 5.0 wt. % to 8.0 wt. %, from 6.0 wt. % to 8.0 wt. %, from 7.0
wt. % to 8.0 wt. %, from 1.0 wt. % to 7.0 wt. %, from 2.0 wt. % to
7.0 wt. %, from 3.0 wt. % to 7.0 wt. %, from 4.0 wt. % to 7.0 wt.
%, from 5.0 wt. % to 7.0 wt. %, from 6.0 wt. % to 7.0 wt. %, from
1.0 wt. % to 6.0 wt. %, from 2.0 wt. % to 6.0 wt. %, from 3.0 wt. %
to 6.0 wt. %, from 4.0 wt. % to 6.0 wt. %, from 5.0 wt. % to 6.0
wt. %, from 1.0 wt. % to 5.0 wt. %, from 2.0 wt. % to 5.0 wt. %,
from 3.0 wt. % to 5.0 wt. %, from 4.0 wt. % to 5.0 wt. %, from 1.0
wt. % to 4.0 wt. %, from 2.0 wt. % to 4.0 wt. %, from 3.0 wt. % to
4.0 wt. %, from 1.0 wt. % to 3.0 wt. %, from 2.0 wt. % to 3.0 wt.
%, or from 1.0 wt. % to 2.0 wt. %. It should be understood that the
solvent and the initiator may be mixed by any suitable process,
such as stirring, blending, agitating, sonicating, and the like.
The mixture of solvent and initiator may, according to embodiments,
be applied to the proppant particle 110 by any suitable process,
such as by spraying the mixture of solvent and initiator onto the
proppant particle 110, dipping the proppant particle 110 into the
mixture of solvent and initiator, and the like. Applying the
initiator to the surface of the proppant particle 110 before the
proppant particle 110 is combined to the mixture of the combination
of monomers and cross-linking agent is added helps polymerization
of the combination of monomers and the cross-linking agent at the
surface of the proppant particle 110.
[0082] According to embodiments, the initiator may be added as a
crystallized or recrystallized initiator to the mixture that
comprises the combination of monomers and the cross-linking agent.
In such embodiments, the initiator is added as a super addition in
relationship to the weight of the combination of monomers and the
cross-linking agent (e.g., if the weight of the combination of
monomers and the cross-linking agent is 100 kg, a 2 wt. % super
addition of the initiator is 2 kg). The initiator may, according to
embodiments, be added to the mixture that comprises the combination
of monomers and the cross-linking agent in an amount from 1.0 wt. %
to 10.0 wt. %, such as from 2.0 wt. % to 10.0 wt. %, from 3.0 wt. %
to 10.0 wt. %, from 4.0 wt. % to 10.0 wt. %, from 5.0 wt. % to 10.0
wt. %, from 6.0 wt. % to 10.0 wt. %, from 7.0 wt. % to 10.0 wt. %,
from 8.0 wt. % to 10.0 wt. %, from 9.0 wt. % to 10.0 wt. %, from
1.0 wt. % to 9.0 wt. %, from 2.0 wt. % to 9.0 wt. %, from 3.0 wt. %
to 9.0 wt. %, from 4.0 wt. % to 9.0 wt. %, from 5.0 wt. % to 9.0
wt. %, from 6.0 wt. % to 9.0 wt. %, from 7.0 wt. % to 9.0 wt. %,
from 8.0 wt. % to 9.0 wt. %, from 1.0 wt. % to 8.0 wt. %, from 2.0
wt. % to 8.0 wt. %, from 3.0 wt. % to 8.0 wt. %, from 4.0 wt. % to
8.0 wt. %, from 5.0 wt. % to 8.0 wt. %, from 6.0 wt. % to 8.0 wt.
%, from 7.0 wt. % to 8.0 wt. %, from 1.0 wt. % to 7.0 wt. %, from
2.0 wt. % to 7.0 wt. %, from 3.0 wt. % to 7.0 wt. %, from 4.0 wt. %
to 7.0 wt. %, from 5.0 wt. % to 7.0 wt. %, from 6.0 wt. % to 7.0
wt. %, from 1.0 wt. % to 6.0 wt. %, from 2.0 wt. % to 6.0 wt. %,
from 3.0 wt. % to 6.0 wt. %, from 4.0 wt. % to 6.0 wt. %, from 5.0
wt. % to 6.0 wt. %, from 1.0 wt. % to 5.0 wt. %, from 2.0 wt. % to
5.0 wt. %, from 3.0 wt. % to 5.0 wt. %, from 4.0 wt. % to 5.0 wt.
%, from 1.0 wt. % to 4.0 wt. %, from 2.0 wt. % to 4.0 wt. %, from
3.0 wt. % to 4.0 wt. %, from 1.0 wt. % to 3.0 wt. %, from 2.0 wt. %
to 3.0 wt. %, or from 1.0 wt. % to 2.0 wt. %. It should be
understood that the initiator, the combination of monomers, and the
cross-linking agent may be mixed by any suitable process, such as
stirring, blending, agitating, sonicating, and the like.
[0083] The combination of the proppant particle 110, combination of
monomers, cross-linking agent, and initiator is well mixed and
heated to a polymerization temperature to begin the polymerization
process that will form the intermediate cross-linked terpolymer
layer 120 on the proppant particle 110. In embodiments, the
polymerization temperature is from 50.degree. C. to 90.degree. C.,
such as from 55.degree. C. to 90.degree. C., from 60.degree. C. to
90.degree. C., from 65.degree. C. to 90.degree. C., from 70.degree.
C. to 90.degree. C., from 75.degree. C. to 90.degree. C., from
80.degree. C. to 90.degree. C., from 85.degree. C. to 90.degree.
C., from 50.degree. C. to 85.degree. C., from 55.degree. C. to
85.degree. C., from 60.degree. C. to 85.degree. C., from 65.degree.
C. to 85.degree. C., from 70.degree. C. to 85.degree. C., from
75.degree. C. to 85.degree. C., from 80.degree. C. to 85.degree.
C., from 50.degree. C. to 80.degree. C., from 55.degree. C. to
80.degree. C., from 60.degree. C. to 80.degree. C., from 65.degree.
C. to 80.degree. C., from 70.degree. C. to 80.degree. C., from
75.degree. C. to 80.degree. C., from 50.degree. C. to 75.degree.
C., from 55.degree. C. to 75.degree. C., from 60.degree. C. to
75.degree. C., from 65.degree. C. to 75.degree. C., from 70.degree.
C. to 75.degree. C., from 50.degree. C. to 70.degree. C., from
55.degree. C. to 70.degree. C., from 60.degree. C. to 70.degree.
C., from 65.degree. C. to 70.degree. C., from 50.degree. C. to
65.degree. C., from 55.degree. C. to 65.degree. C., from 60.degree.
C. to 65.degree. C., from 50.degree. C. to 60.degree. C., from
55.degree. C. to 60.degree. C., or from 50.degree. C. to 55.degree.
C.
[0084] The combination of the proppant particle 110, combination of
monomers, cross-linking agent, and initiator may, according to
embodiments, be held at the polymerization temperature for a
duration that is from 12 hours to 60 hours, such as from 16 hours
to 60 hours, from 20 hours to 60 hours, from 24 hours to 60 hours,
from 28 hours to 60 hours, from 32 hours to 60 hours, from 36 hours
to 60 hours, from 40 hours to 60 hours, from 44 hours to 60 hours,
from 48 hours to 60 hours, from 52 hours to 60 hours, from 56 hours
to 60 hours, from 12 hours to 56 hours, from 16 hours to 56 hours,
from 20 hours to 56 hours, from 24 hours to 56 hours, from 28 hours
to 56 hours, from 32 hours to 56 hours, from 36 hours to 56 hours,
from 40 hours to 56 hours, from 44 hours to 56 hours, from 48 hours
to 56 hours, from 52 hours to 56 hours, from 12 hours to 52 hours,
from 16 hours to 52 hours, from 20 hours to 52 hours, from 24 hours
to 52 hours, from 28 hours to 52 hours, from 32 hours to 52 hours,
from 36 hours to 52 hours, from 40 hours to 52 hours, from 44 hours
to 52 hours, from 48 hours to 52 hours, from 12 hours to 48 hours,
from 16 hours to 48 hours, from 20 hours to 48 hours, from 24 hours
to 48 hours, from 28 hours to 48 hours, from 32 hours to 48 hours,
from 36 hours to 48 hours, from 40 hours to 48 hours, from 44 hours
to 48 hours, from 12 hours to 44 hours, from 16 hours to 44 hours,
from 20 hours to 44 hours, from 24 hours to 44 hours, from 28 hours
to 44 hours, from 32 hours to 44 hours, from 36 hours to 44 hours,
from 40 hours to 44 hours, from 12 hours to 40 hours, from 16 hours
to 40 hours, from 20 hours to 40 hours, from 24 hours to 40 hours,
from 28 hours to 40 hours, from 32 hours to 40 hours, from 36 hours
to 40 hours, from 12 hours to 36 hours, from 16 hours to 36 hours,
from 20 hours to 36 hours, from 24 hours to 36 hours, from 28 hours
to 36 hours, from 32 hours to 36 hours, from 12 hours to 32 hours,
from 16 hours to 32 hours, from 20 hours to 32 hours, from 24 hours
to 32 hours, from 28 hours to 32 hours, from 12 hours to 28 hours,
from 16 hours to 28 hours, from 20 hours to 28 hours, from 24 hours
to 28 hours, from 12 hours to 24 hours, from 16 hours to 24 hours,
from 20 hours to 24 hours, from 12 hours to 20 hours, from 16 hours
to 20 hours, or from 12 hours to 16 hours.
[0085] It should be understood that, in embodiments, after the
polymerization process has been completed, the initiator is not
present in the final structure of the intermediate cross-linked
terpolymer layer 120.
[0086] Without being bound by any particular theory, by forming an
intermediate cross-linked terpolymer layer 120 as previously
described, a polymer layer having a 3D structure is formed on the
proppant particle 110. When a combination of monomers as previously
described are combined with a cross-linking agent and an initiator,
the initiator changes into radicals under the heating conditions.
With the aid of initiator radicals, the monomer molecules are
synchronously transformed into monomer and cross-linker free
radicals. Thereafter, the monomer and cross-linker free radicals
are turned into radical donors to the neighboring monomer molecules
and the cross-linking agent. Consequently, a random addition
copolymerization between the combination of monomers takes place to
produce polymer chain radicals, resulting in the growth of
co-polymer radicals. During the course of chain propagation, the
growing chains may also randomly react with the cross-linker
radicals. As a result, an interpenetrating and 3D-cross-linked
polymer network structures are eventually formed.
[0087] As a specific example, and according to embodiments where
the combination of monomers is a combination of styrene and methyl
methacrylate, the cross-linking agent is divinyl benzene, and the
initiator is AIBN, the 3D-cross-linked PS-PMMA/DVB polymer layer
having a 3D-cross-linked network structure for the PS-PMMA/DVB is
depicted in FIG. 2.
[0088] The density of the 3D-network structure of the intermediate
cross-linked terpolymer layer 120 is greatly influenced by the
concentration during of the cross-linking agent present the
preparation. When the cross-linking agent concentration is
increased, the crosslinking densities of the resulting polymer are
also increased, as is confirmed by thermal and mechanical analysis.
For instance, the increased crosslinking densities resulting from
greater amounts of cross-linking agent present during the
preparation of the intermediate cross-linked terpolymer layer 120
may be confirmed by an increase in the degradation temperature
(Tdeg) of the intermediate cross-linked terpolymer layer 120.
[0089] Subsequent to the formation of the intermediate cross-linked
terpolymer layer 120 on the proppant particle 110, an outer resin
layer 130 that directly or indirectly encapsulates the intermediate
cross-linked terpolymer layer 120 is formed. The outer resin layer
130 is formed from a combination of epoxy resin, a curing agent,
and graphene. Initially, the epoxy resin and curing agent are mixed
together.
[0090] The epoxy resin that is used in the outer resin layer 130
according to embodiments has the following general formula:
##STR00004##
Where R and R' are selected from the group consisting of a part of
a six-membered ring, a polyhydroxyphenol, a polybasic acid, a
polyol, and combinations thereof. In embodiments, the epoxy resin
may be a bisphenol A epoxy resin having the following formula:
##STR00005##
[0091] The curing agent may be any amine functional curing agent.
According to embodiments, the curing agent is selected from the
group consisting of aliphatic polyamines and their derivatives,
modified aliphatic amines, aromatic amines, and combinations
thereof.
[0092] The amount of epoxy resin in the combination of epoxy resin
and curing agent is, according to embodiments, from 15.0 wt. % to
90.0 wt. %, such as from 20.0 wt. % to 90.0 wt. %, from 25.0 wt. %
to 90.0 wt. %, from 30.0 wt. % to 90.0 wt. %, from 35.0 wt. % to
90.0 wt. %, from 40.0 wt. % to 90.0 wt. %, from 45.0 wt. % to 90.0
wt. %, from 50.0 wt. % to 90.0 wt. %, from 55.0 wt. % to 90.0 wt.
%, from 60.0 wt. % to 90.0 wt. %, from 65.0 wt. % to 90.0 wt. %,
from 70.0 wt. % to 90.0 wt. %, from 75.0 wt. % to 90.0 wt. %, from
80.0 wt. % to 90.0 wt. %, from 85.0 wt. % to 90.0 wt. %, from 15.0
wt. % to 85.0 wt. %, from 20.0 wt. % to 85.0 wt. %, from 25.0 wt. %
to 85.0 wt. %, from 30.0 wt. % to 85.0 wt. %, from 35.0 wt. % to
85.0 wt. %, from 40.0 wt. % to 85.0 wt. %, from 45.0 wt. % to 85.0
wt. %, from 50.0 wt. % to 85.0 wt. %, from 55.0 wt. % to 85.0 wt.
%, from 60.0 wt. % to 85.0 wt. %, from 65.0 wt. % to 85.0 wt. %,
from 70.0 wt. % to 85.0 wt. %, from 75.0 wt. % to 85.0 wt. %, from
80.0 wt. % to 85.0 wt. %, from 15.0 wt. % to 80.0 wt. %, from 20.0
wt. % to 80.0 wt. %, from 25.0 wt. % to 80.0 wt. %, from 30.0 wt. %
to 80.0 wt. %, from 35.0 wt. % to 80.0 wt. %, from 40.0 wt. % to
80.0 wt. %, from 45.0 wt. % to 80.0 wt. %, from 50.0 wt. % to 80.0
wt. %, from 55.0 wt. % to 80.0 wt. %, from 60.0 wt. % to 80.0 wt.
%, from 65.0 wt. % to 80.0 wt. %, from 70.0 wt. % to 80.0 wt. %,
from 75.0 wt. % to 80.0 wt. %, from 15.0 wt. % to 75.0 wt. %, from
20.0 wt. % to 75.0 wt. %, from 25.0 wt. % to 75.0 wt. %, from 30.0
wt. % to 75.0 wt. %, from 35.0 wt. % to 75.0 wt. %, from 40.0 wt. %
to 75.0 wt. %, from 45.0 wt. % to 75.0 wt. %, from 50.0 wt. % to
75.0 wt. %, from 55.0 wt. % to 75.0 wt. %, from 60.0 wt. % to 75.0
wt. %, from 65.0 wt. % to 75.0 wt. %, from 70.0 wt. % to 75.0 wt.
%, from 15.0 wt. % to 70.0 wt. %, from 20.0 wt. % to 70.0 wt. %,
from 25.0 wt. % to 70.0 wt. %, from 30.0 wt. % to 70.0 wt. %, from
35.0 wt. % to 70.0 wt. %, from 40.0 wt. % to 70.0 wt. %, from 45.0
wt. % to 70.0 wt. %, from 50.0 wt. % to 70.0 wt. %, from 55.0 wt. %
to 70.0 wt. %, from 60.0 wt. % to 70.0 wt. %, from 65.0 wt. % to
70.0 wt. %, from 15.0 wt. % to 65.0 wt. %, from 20.0 wt. % to 65.0
wt. %, from 25.0 wt. % to 65.0 wt. %, from 30.0 wt. % to 65.0 wt.
%, from 35.0 wt. % to 65.0 wt. %, from 40.0 wt. % to 65.0 wt. %,
from 45.0 wt. % to 65.0 wt. %, from 50.0 wt. % to 65.0 wt. %, from
55.0 wt. % to 65.0 wt. %, from 60.0 wt. % to 65.0 wt. %, from 15.0
wt. % to 60.0 wt. %, from 20.0 wt. % to 60.0 wt. %, from 25.0 wt. %
to 60.0 wt. %, from 30.0 wt. % to 60.0 wt. %, from 35.0 wt. % to
60.0 wt. %, from 40.0 wt. % to 60.0 wt. %, from 45.0 wt. % to 60.0
wt. %, from 50.0 wt. % to 60.0 wt. %, from 55.0 wt. % to 60.0 wt.
%, from 15.0 wt. % to 55.0 wt. %, from 20.0 wt. % to 55.0 wt. %,
from 25.0 wt. % to 55.0 wt. %, from 30.0 wt. % to 55.0 wt. %, from
35.0 wt. % to 55.0 wt. %, from 40.0 wt. % to 55.0 wt. %, from 45.0
wt. % to 55.0 wt. %, from 50.0 wt. % to 55.0 wt. %, from 15.0 wt. %
to 50.0 wt. %, from 20.0 wt. % to 50.0 wt. %, from 25.0 wt. % to
50.0 wt. %, from 30.0 wt. % to 50.0 wt. %, from 35.0 wt. % to 50.0
wt. %, from 40.0 wt. % to 50.0 wt. %, from 45.0 wt. % to 50.0 wt.
%, from 15.0 wt. % to 45.0 wt. %, from 20.0 wt. % to 45.0 wt. %,
from 25.0 wt. % to 45.0 wt. %, from 30.0 wt. % to 45.0 wt. %, from
35.0 wt. % to 45.0 wt. %, from 40.0 wt. % to 45.0 wt. %, from 15.0
wt. % to 40.0 wt. %, from 20.0 wt. % to 40.0 wt. %, from 25.0 wt. %
to 40.0 wt. %, from 30.0 wt. % to 40.0 wt. %, from 35.0 wt. % to
40.0 wt. %, from 15.0 wt. % to 35.0 wt. %, from 20.0 wt. % to 35.0
wt. %, from 25.0 wt. % to 35.0 wt. %, from 30.0 wt. % to 35.0 wt.
%, from 15.0 wt. % to 30.0 wt. %, from 20.0 wt. % to 30.0 wt. %,
from 25.0 wt. % to 30.0 wt. %, from 15.0 wt. % to 25.0 wt. %, from
20.0 wt. % to 25.0 wt. %, or from 15.0 wt. % to 20.0 wt. %.
[0093] According to embodiments, the curing agent may be present in
the combination of epoxy resin and curing agent in amounts from
10.0 wt. % to 85.0 wt. %, such as from 15.0 wt. % to 85.0 wt. %,
from 20.0 wt. % to 85.0 wt. %, from 25.0 wt. % to 85.0 wt. %, from
30.0 wt. % to 85.0 wt. %, from 35.0 wt. % to 85.0 wt. %, from 40.0
wt. % to 85.0 wt. %, from 45.0 wt. % to 85.0 wt. %, from 50.0 wt. %
to 85.0 wt. %, from 55.0 wt. % to 85.0 wt. %, from 60.0 wt. % to
85.0 wt. %, from 65.0 wt. % to 85.0 wt. %, from 70.0 wt. % to 85.0
wt. %, from 75.0 wt. % to 85.0 wt. %, from 80.0 wt. % to 85.0 wt.
%, from 10.0 wt. % to 80.0 wt. %, from 15.0 wt. % to 80.0 wt. %,
from 20.0 wt. % to 80.0 wt. %, from 25.0 wt. % to 80.0 wt. %, from
30.0 wt. % to 80.0 wt. %, from 35.0 wt. % to 80.0 wt. %, from 40.0
wt. % to 80.0 wt. %, from 45.0 wt. % to 80.0 wt. %, from 50.0 wt. %
to 80.0 wt. %, from 55.0 wt. % to 80.0 wt. %, from 60.0 wt. % to
80.0 wt. %, from 65.0 wt. % to 80.0 wt. %, from 70.0 wt. % to 80.0
wt. %, from 75.0 wt. % to 80.0 wt. %, from 10.0 wt. % to 75.0 wt.
%, from 15.0 wt. % to 75.0 wt. %, from 20.0 wt. % to 75.0 wt. %,
from 25.0 wt. % to 75.0 wt. %, from 30.0 wt. % to 75.0 wt. %, from
35.0 wt. % to 75.0 wt. %, from 40.0 wt. % to 75.0 wt. %, from 45.0
wt. % to 75.0 wt. %, from 50.0 wt. % to 75.0 wt. %, from 55.0 wt. %
to 75.0 wt. %, from 60.0 wt. % to 75.0 wt. %, from 65.0 wt. % to
75.0 wt. %, from 70.0 wt. % to 75.0 wt. %, from 10.0 wt. % to 70.0
wt. %, from 15.0 wt. % to 70.0 wt. %, from 20.0 wt. % to 70.0 wt.
%, from 25.0 wt. % to 70.0 wt. %, from 30.0 wt. % to 70.0 wt. %,
from 35.0 wt. % to 70.0 wt. %, from 40.0 wt. % to 70.0 wt. %, from
45.0 wt. % to 70.0 wt. %, from 50.0 wt. % to 70.0 wt. %, from 55.0
wt. % to 70.0 wt. %, from 60.0 wt. % to 70.0 wt. %, from 65.0 wt. %
to 70.0 wt. %, from 10.0 wt. % to 65.0 wt. %, from 15.0 wt. % to
65.0 wt. %, from 20.0 wt. % to 65.0 wt. %, from 25.0 wt. % to 65.0
wt. %, from 30.0 wt. % to 65.0 wt. %, from 35.0 wt. % to 65.0 wt.
%, from 40.0 wt. % to 65.0 wt. %, from 45.0 wt. % to 65.0 wt. %,
from 50.0 wt. % to 65.0 wt. %, from 55.0 wt. % to 65.0 wt. %, from
60.0 wt. % to 65.0 wt. %, from 10.0 wt. % to 60.0 wt. %, from 15.0
wt. % to 60.0 wt. %, from 20.0 wt. % to 60.0 wt. %, from 25.0 wt. %
to 60.0 wt. %, from 30.0 wt. % to 60.0 wt. %, from 35.0 wt. % to
60.0 wt. %, from 40.0 wt. % to 60.0 wt. %, from 45.0 wt. % to 60.0
wt. %, from 50.0 wt. % to 60.0 wt. %, from 55.0 wt. % to 60.0 wt.
%, from 10.0 wt. % to 55.0 wt. %, from 15.0 wt. % to 55.0 wt. %,
from 20.0 wt. % to 55.0 wt. %, from 25.0 wt. % to 55.0 wt. %, from
30.0 wt. % to 55.0 wt. %, from 35.0 wt. % to 55.0 wt. %, from 40.0
wt. % to 55.0 wt. %, from 45.0 wt. % to 55.0 wt. %, from 50.0 wt. %
to 55.0 wt. %, from 10.0 wt. % to 50.0 wt. %, from 15.0 wt. % to
50.0 wt. %, from 20.0 wt. % to 50.0 wt. %, from 25.0 wt. % to 50.0
wt. %, from 30.0 wt. % to 50.0 wt. %, from 35.0 wt. % to 50.0 wt.
%, from 40.0 wt. % to 50.0 wt. %, from 45.0 wt. % to 50.0 wt. %,
from 10.0 wt. % to 45.0 wt. %, from 15.0 wt. % to 45.0 wt. %, from
20.0 wt. % to 45.0 wt. %, from 25.0 wt. % to 45.0 wt. %, from 30.0
wt. % to 45.0 wt. %, from 35.0 wt. % to 45.0 wt. %, from 40.0 wt. %
to 45.0 wt. %, from 10.0 wt. % to 40.0 wt. %, from 15.0 wt. % to
40.0 wt. %, from 20.0 wt. % to 40.0 wt. %, from 25.0 wt. % to 40.0
wt. %, from 30.0 wt. % to 40.0 wt. %, from 35.0 wt. % to 40.0 wt.
%, from 10.0 wt. % to 35.0 wt. %, from 15.0 wt. % to 35.0 wt. %,
from 20.0 wt. % to 35.0 wt. %, from 25.0 wt. % to 35.0 wt. %, from
30.0 wt. % to 35.0 wt. %, from 10.0 wt. % to 30.0 wt. %, from 15.0
wt. % to 30.0 wt. %, from 20.0 wt. % to 30.0 wt. %, from 25.0 wt. %
to 30.0 wt. %, from 10.0 wt. % to 25.0 wt. %, from 15.0 wt. % to
25.0 wt. %, from 20.0 wt. % to 25.0 wt. %, from 10.0 wt. % to 20.0
wt. %, from 15.0 wt. % to 20.0 wt. %, or from 10.0 wt. % to 15.0
wt. %. It should be understood that the epoxy resin and curing
agent may be mixed together by any suitable, physical mixing
process, such as stirring, blending, agitating, sonicating, and the
like.
[0094] Once the epoxy resin and curing agent are combined, graphene
is added to the combination of epoxy resin and curing agent.
According to embodiments, the graphene used in the outer resin
layer 130 has a thickness from 6.0 nm to 8.0 nm, such as from 6.5
nm to 8.0 nm, from 7.0 nm to 8.0 nm, from 7.5 nm to 8.0 nm, from
6.5 nm to 7.5 nm, from 7.0 nm to 7.5 nm, or from 6.5 nm to 7.0 nm.
According to embodiments, the graphene used in the outer resin
layer 130 has a surface area from 120 m2/g to 150 m2/g, such as
from 125 m2/g to 150 m2/g, from 130 m2/g to 150 m2/g, from 135 m2/g
to 150 m2/g, from 140 m2/g to 150 m2/g, from 145 m2/g to 150 m2/g,
from 120 m2/g to 145 m2/g, from 125 m2/g to 145 m2/g, from 130 m2/g
to 145 m2/g, from 135 m2/g to 145 m2/g, from 140 m2/g to 145 m2/g,
from 120 m2/g to 140 m2/g, from 125 m2/g to 140 m2/g, from 130 m2/g
to 140 m2/g, from 135 m2/g to 140 m2/g, from 120 m2/g to 135 m2/g,
from 125 m2/g to 135 m2/g, from 130 m2/g to 135 m2/g, from 120 m2/g
to 130 m2/g, from 125 m2/g to 130 m2/g, or from 120 m2/g to 125
m2/g. According to embodiments, the graphene used in the outer
resin layer 130 has an average particle size from 15 .mu.m to 35
.mu.m, such as from 20 .mu.m to 35 .mu.m, from 25 .mu.m to 35
.mu.m, from 30 .mu.m to 35 .mu.m, from 15 .mu.m to 30 .mu.m, from
20 .mu.m to 30 .mu.m, from 25 .mu.m to 30 .mu.m, from 15 .mu.m to
25 .mu.m, from 20 .mu.m to 25 .mu.m, or from 15 .mu.m to 20 .mu.m.
According to embodiments, the graphene used in the outer resin
layer 130 has a bulk density from 0.03 g/cc to 0.10 g/cc, such as
from 0.05 g/cc to 0.10 g/cc, from 0.07 g/cc to 0.10 g/cc, from 0.03
g/cc to 0.07 g/cc, from 0.05 g/cc to 0.07 g/cc, or from 0.03 g/cc
to 0.05 g/cc. According to embodiments, the graphene used in the
outer resin layer 130 has a thermal conductivity from 2500 W/(m K)
to 3500 W/(m K), such as from 2750 W/(m K) to 3500 W/(m K), from
3000 W/(m K) to 3500 W/(m K), from 3250 W/(m K) to 3500 W/(m K),
from 2500 W/(m K) to 3250 W/(m K), from 2750 W/(m K) to 3250 W/(m
K), from 3000 W/(m K) to 3250 W/(m K), from 2500 W/(m K) to 3000
W/(m K), from 2750 W/(m K) to 3000 W/(m K), or from 2500 W/(m K) to
2750 W/(m K). According to embodiments, the graphene used in the
outer resin layer 130 has a tensile strength from 2.0 MPa to 7.0
MPa, such as from 2.5 MPa to 7.0 MPa, from 3.0 MPa to 7.0 MPa, from
3.5 MPa to 7.0 MPa, from 4.0 MPa to 7.0 MPa, from 4.5 MPa to 7.0
MPa, from 5.0 MPa to 7.0 MPa, from 5.5 MPa to 7.0 MPa, from 6.0 MPa
to 7.0 MPa, from 6.5 MPa to 7.0 MPa, from 2.0 MPa to 6.5 MPa, from
2.5 MPa to 6.5 MPa, from 3.0 MPa to 6.5 MPa, from 3.5 MPa to 6.5
MPa, from 4.0 MPa to 6.5 MPa, from 4.5 MPa to 6.5 MPa, from 5.0 MPa
to 6.5 MPa, from 5.5 MPa to 6.5 MPa, from 6.0 MPa to 6.5 MPa, from
2.0 MPa to 6.0 MPa, from 2.5 MPa to 6.0 MPa, from 3.0 MPa to 6.0
MPa, from 3.5 MPa to 6.0 MPa, from 4.0 MPa to 6.0 MPa, from 4.5 MPa
to 6.0 MPa, from 5.0 MPa to 6.0 MPa, from 5.5 MPa to 6.0 MPa, from
2.0 MPa to 5.5 MPa, from 2.5 MPa to 5.5 MPa, from 3.0 MPa to 5.5
MPa, from 3.5 MPa to 5.5 MPa, from 4.0 MPa to 5.5 MPa, from 4.5 MPa
to 5.5 MPa, from 5.0 MPa to 5.5 MPa, from 2.0 MPa to 5.0 MPa, from
2.5 MPa to 5.0 MPa, from 3.0 MPa to 5.0 MPa, from 3.5 MPa to 5.0
MPa, from 4.0 MPa to 5.0 MPa, from 4.5 MPa to 5.0 MPa, from 2.0 MPa
to 4.5 MPa, from 2.5 MPa to 4.5 MPa, from 3.0 MPa to 4.5 MPa, from
3.5 MPa to 4.5 MPa, from 4.0 MPa to 4.5 MPa, from 2.0 MPa to 4.0
MPa, from 2.5 MPa to 4.0 MPa, from 3.0 MPa to 4.0 MPa, from 3.5 MPa
to 4.0 MPa, from 2.0 MPa to 3.5 MPa, from 2.5 MPa to 3.5 MPa, from
3.0 MPa to 3.5 MPa, from 2.0 MPa to 3.0 MPa, from 2.5 MPa to 3.0
MPa, from 2.0 MPa to 2.5 MPa. According to embodiments, the
graphene used in the outer resin layer 130 has an electrical
conductivity from 0.50.times.107 S/m to 1.50.times.10 7 S/m, such
as from 0.75.times.107 S/m to 1.50.times.10 7 S/m, from
1.00.times.107 S/m to 1.50.times.10 7 S/m, from 1.25.times.107 S/m
to 1.50.times.10 7 S/m, from 0.50.times.107 S/m to 1.25.times.10 7
S/m, from 0.75.times.107 S/m to 1.25.times.10 7 S/m, from
1.00.times.107 S/m to 1.25.times.10 7 S/m, from 0.50.times.107 S/m
to 1.00.times.10 7 S/m, from 0.75.times.107 S/m to 1.00.times.10 7
S/m, or from 0.50.times.107 S/m to 0.75.times.10 7 S/m. According
to some embodiments, the graphene used in the outer resin layer 130
is XGNP-M-25 Graphene Nanoplatelets manufactured by XG
Sciences.
[0095] According to one or more embodiments, the graphene is added
to the combination of epoxy resin and curing agent as a super
addition relative to the combination of epoxy resin and curing
agent. In embodiments, the graphene may be added as a super
addition in amounts from 0.05 wt. % to 0.50 wt. %, such as from
0.10 wt. % to 0.50 wt. %, from 0.15 wt. % to 0.50 wt. %, from 0.20
wt. % to 0.50 wt. %, from 0.25 wt. % to 0.50 wt. %, from 0.30 wt. %
to 0.50 wt. %, from 0.35 wt. % to 0.50 wt. %, from 0.40 wt. % to
0.50 wt. %, from 0.45 wt. % to 0.50 wt. %, from 0.05 wt. % to 0.45
wt. %, from 0.10 wt. % to 0.45 wt. %, from 0.15 wt. % to 0.45 wt.
%, from 0.20 wt. % to 0.45 wt. %, from 0.25 wt. % to 0.45 wt. %,
from 0.30 wt. % to 0.45 wt. %, from 0.35 wt. % to 0.45 wt. %, from
0.40 wt. % to 0.45 wt. %, from 0.05 wt. % to 0.40 wt. %, from 0.10
wt. % to 0.40 wt. %, from 0.15 wt. % to 0.40 wt. %, from 0.20 wt. %
to 0.40 wt. %, from 0.25 wt. % to 0.40 wt. %, from 0.30 wt. % to
0.40 wt. %, from 0.35 wt. % to 0.40 wt. %, from 0.05 wt. % to 0.35
wt. %, from 0.10 wt. % to 0.35 wt. %, from 0.15 wt. % to 0.35 wt.
%, from 0.20 wt. % to 0.35 wt. %, from 0.25 wt. % to 0.35 wt. %,
from 0.30 wt. % to 0.35 wt. %, from 0.05 wt. % to 0.30 wt. %, from
0.10 wt. % to 0.30 wt. %, from 0.15 wt. % to 0.30 wt. %, from 0.20
wt. % to 0.30 wt. %, from 0.25 wt. % to 0.30 wt. %, from 0.05 wt. %
to 0.25 wt. %, from 0.10 wt. % to 0.25 wt. %, from 0.15 wt. % to
0.25 wt. %, from 0.20 wt. % to 0.25 wt. %, from 0.05 wt. % to 0.20
wt. %, from 0.10 wt. % to 0.20 wt. %, from 0.15 wt. % to 0.20 wt.
%, from 0.05 wt. % to 0.15 wt. %, from 0.10 wt. % to 0.15 wt. %, or
from 0.05 wt. % to 0.10 wt. %. It should be understood that the
combination of epoxy resin and curing agent may be mixed with the
graphene by any suitable, physical mixing process, such as
stirring, blending, agitating, sonicating, and the like.
[0096] The combination of epoxy resin, curing agent, and graphene
are added to proppant particles 110 encapsulated in an intermediate
cross-linked terpolymer layer 120. It should be understood that the
combination of epoxy resin, curing agent, and graphene may be mixed
with the encapsulated proppant particles by any suitable, physical
mixing process, such as stirring, blending, agitating, sonicating,
and the like. Subsequent to mixing, the encapsulated proppant
particles having the combination of epoxy resin, curing agent, and
graphene on their outermost surface are heated to a curing
temperature to cure the epoxy resin. According to embodiments, the
curing temperature is from 100.degree. C. to 200.degree. C., such
as from 110.degree. C. to 200.degree. C., from 120.degree. C. to
200.degree. C., from 130.degree. C. to 200.degree. C., from
140.degree. C. to 200.degree. C., from 150.degree. C. to
200.degree. C., from 160.degree. C. to 200.degree. C., from
170.degree. C. to 200.degree. C., from 180.degree. C. to
200.degree. C., from 190.degree. C. to 200.degree. C., from
100.degree. C. to 190.degree. C., from 110.degree. C. to
190.degree. C., from 120.degree. C. to 190.degree. C., from
130.degree. C. to 190.degree. C., from 140.degree. C. to
190.degree. C., from 150.degree. C. to 190.degree. C., from
160.degree. C. to 190.degree. C., from 170.degree. C. to
190.degree. C., from 180.degree. C. to 190.degree. C., from
100.degree. C. to 180.degree. C., from 110.degree. C. to
180.degree. C., from 120.degree. C. to 180.degree. C., from
130.degree. C. to 180.degree. C., from 140.degree. C. to
180.degree. C., from 150.degree. C. to 180.degree. C., from
160.degree. C. to 180.degree. C., from 170.degree. C. to
180.degree. C., from 100.degree. C. to 170.degree. C., from
110.degree. C. to 170.degree. C., from 120.degree. C. to
170.degree. C., from 130.degree. C. to 170.degree. C., from
140.degree. C. to 170.degree. C., from 150.degree. C. to
170.degree. C., from 160.degree. C. to 170.degree. C., from
100.degree. C. to 160.degree. C., from 110.degree. C. to
160.degree. C., from 120.degree. C. to 160.degree. C., from
130.degree. C. to 160.degree. C., from 140.degree. C. to
160.degree. C., from 150.degree. C. to 160.degree. C., from
100.degree. C. to 150.degree. C., from 110.degree. C. to
150.degree. C., from 120.degree. C. to 150.degree. C., from
130.degree. C. to 150.degree. C., from 140.degree. C. to
150.degree. C., from 100.degree. C. to 140.degree. C., from
110.degree. C. to 140.degree. C., from 120.degree. C. to
140.degree. C., from 130.degree. C. to 140.degree. C., from
100.degree. C. to 130.degree. C., from 110.degree. C. to
130.degree. C., from 120.degree. C. to 130.degree. C., from
100.degree. C. to 120.degree. C., from 110.degree. C. to
120.degree. C., or from 100.degree. C. to 110.degree. C.
[0097] According to embodiments, the encapsulated proppant
particles having the combination of epoxy resin, curing agent, and
graphene on their outermost surface may be held at the curing
temperature for a time from 1 minute to 20 minutes, such as from 2
minutes to 20 minutes, from 5 minutes to 20 minutes, from 7 minutes
to 20 minutes, from 10 minutes to 20 minutes, from 12 minutes to 20
minutes, from 15 minutes to 20 minutes, from 17 minutes to 20
minutes, from 1 minute to 17 minutes, from 2 minutes to 17 minutes,
from 5 minutes to 17 minutes, from 7 minutes to 17 minutes, from 10
minutes to 17 minutes, from 12 minutes to 17 minutes, from 15
minutes to 17 minutes, from 1 minute to 15 minutes, from 2 minutes
to 15 minutes, from 5 minutes to 15 minutes, from 7 minutes to 15
minutes, from 10 minutes to 15 minutes, from 12 minutes to 15
minutes, from 1 minute to 12 minutes, from 2 minutes to 12 minutes,
from 5 minutes to 12 minutes, from 7 minutes to 12 minutes, from 10
minutes to 12 minutes, from 1 minute to 10 minutes, from 2 minutes
to 10 minutes, from 5 minutes to 10 minutes, from 7 minutes to 10
minutes, from 1 minute to 7 minutes, from 2 minutes to 7 minutes,
from 5 minutes to 7 minutes, from 1 minute to 5 minutes, from 2
minutes to 5 minutes, or from 1 minute to 2 minutes.
[0098] The reaction mechanism for curing the epoxy resin may,
according to one or more embodiments, be as follows:
##STR00006##
[0099] Accordingly, the outer resin layer 130 of the coated
proppant 100 comprises a cured resin, which is formed from a
reaction between the curing agent and the epoxy resin, and
graphene.
[0100] Properties of proppant particles with coatings as previously
disclosed and described will now be described. Four test methods
for determining the properties of proppant particles with coatings
as previously disclosed and described were used; Crush Test,
Nanoindentation, Thermal Analysis, and Optical Tests. Each of these
methods and the properties of proppant particles with coatings as
previously disclosed and described are subsequently disclosed.
[0101] The Crush Test utilizes a hydraulic load frame with stress
levels up to 103 MPa (15000 psi) to test the crush resistance of
the proppant particles with coatings as previously disclosed and
described. Confined compression tests on the proppants are carried
out following the American Petroleum Institute (API RP 60)
standard. The size of the proppant particles is 40/70 mesh. The
proppant sample was firstly sieved using a 40-mesh sieve so that
all tested proppant particles are within the specified size range
of 40 mesh. Then, the proppant samples were applied specific stress
ranging from 3000 psi to 10000 psi for a period of 2 min. The
crushed (damaged) proppant at each stress level is then sieved
using the same sieve (40 mesh) to collect the remains and fine
(size less than 40 mesh). The fine production (%) was calculated
(equation e) from the damaged proppants of size less than 40
mesh.
Fine .times. .times. production .times. .times. ( % ) = Amount
.times. .times. of .times. .times. Fine .times. .times. ( g )
Original .times. .times. weight .times. .times. of .times. .times.
Proppant .times. .times. ( g ) .times. 1 .times. 0 .times. 0
Equation .times. .times. ( 2 ) ##EQU00002##
[0102] Generally, having a fine production of 10% or less is
acceptable. However, as the load on the proppant increases, such as
the further into the subsurface formation the proppant traverses,
the fine production also increases. However, proppant particles
with coatings as previously disclosed and described are able to
withstand increased loads, as evidenced by decreased fine
production even at greater loads. According to embodiments, at a
load of 12000 psi, the coated proppant particle has a fine
production from 2.0% to 10.0%, from 2.5% to 10.0%, from 3.0% to
10.0%, from 3.5% to 10.0%, from 4.0% to 10.0%, from 4.5% to 10.0%,
from 5.0% to 10.0%, from 5.5% to 10.0%, from 6.0% to 10.0%, from
6.5% to 10.0%, from 7.0% to 10.0%, from 7.5% to 10.0%, from 8.0% to
10.0%, from 8.5% to 10.0%, from 9.0% to 10.0%, from 9.5% to 10.0%,
from 2.0% to 9.5%, from 2.5% to 9.5%, from 3.0% to 9.5%, from 3.5%
to 9.5%, from 4.0% to 9.5%, from 4.5% to 9.5%, from 5.0% to 9.5%,
from 5.5% to 9.5%, from 6.0% to 9.5%, from 6.5% to 9.5%, from 7.0%
to 9.5%, from 7.5% to 9.5%, from 8.0% to 9.5%, from 8.5% to 9.5%,
from 9.0% to 9.5%, from 2.0% to 9.0%, from 2.5% to 9.0%, from 3.0%
to 9.0%, from 3.5% to 9.0%, from 4.0% to 9.0%, from 4.5% to 9.0%,
from 5.0% to 9.0%, from 5.5% to 9.0%, from 6.0% to 9.0%, from 6.5%
to 9.0%, from 7.0% to 9.0%, from 7.5% to 9.0%, from 8.0% to 9.0%,
from 8.5% to 9.0%, from 2.0% to 8.5%, from 2.5% to 8.5%, from 3.0%
to 8.5%, from 3.5% to 8.5%, from 4.0% to 8.5%, from 4.5% to 8.5%,
from 5.0% to 8.5%, from 5.5% to 8.5%, from 6.0% to 8.5%, from 6.5%
to 8.5%, from 7.0% to 8.5%, from 7.5% to 8.5%, from 8.0% to 8.5%,
from 2.0% to 8.0%, from 2.5% to 8.0%, from 3.0% to 8.0%, from 3.5%
to 8.0%, from 4.0% to 8.0%, from 4.5% to 8.0%, from 5.0% to 8.0%,
from 5.5% to 8.0%, from 6.0% to 8.0%, from 6.5% to 8.0%, from 7.0%
to 8.0%, from 7.5% to 8.0%, from 2.0% to 7.5%, from 2.5% to 7.5%,
from 3.0% to 7.5%, from 3.5% to 7.5%, from 4.0% to 7.5%, from 4.5%
to 7.5%, from 5.0% to 7.5%, from 5.5% to 7.5%, from 6.0% to 7.5%,
from 6.5% to 7.5%, from 7.0% to 7.5%, from 2.0% to 7.0%, from 2.5%
to 7.0%, from 3.0% to 7.0%, from 3.5% to 7.0%, from 4.0% to 7.0%,
from 4.5% to 7.0%, from 5.0% to 7.0%, from 5.5% to 7.0%, from 6.0%
to 7.0%, from 6.5% to 7.0%, from 2.0% to 6.5%, from 2.5% to 6.5%,
from 3.0% to 6.5%, from 3.5% to 6.5%, from 4.0% to 6.5%, from 4.5%
to 6.5%, from 5.0% to 6.5%, from 5.5% to 6.5%, from 6.0% to 6.5%,
from 2.0% to 6.0%, from 2.5% to 6.0%, from 3.0% to 6.0%, from 3.5%
to 6.0%, from 4.0% to 6.0%, from 4.5% to 6.0%, from 5.0% to 6.0%,
from 5.5% to 6.0%, from 2.0% to 5.5%, from 2.5% to 5.5%, from 3.0%
to 5.5%, from 3.5% to 5.5%, from 4.0% to 5.5%, from 4.5% to 5.5%,
from 5.0% to 5.5%, from 2.0% to 5.0%, from 2.5% to 5.0%, from 3.0%
to 5.0%, from 3.5% to 5.0%, from 4.0% to 5.0%, from 4.5% to 5.0%,
from 2.0% to 4.5%, from 2.5% to 4.5%, from 3.0% to 4.5%, from 3.5%
to 4.5%, from 4.0% to 4.5%, from 2.0% to 4.0%, from 2.5% to 4.0%,
from 3.0% to 4.0%, from 3.5% to 4.0%, from 2.0% to 3.5%, from 2.5%
to 3.5%, from 3.0% to 3.5%, from 2.0% to 3.0%, from 2.5% to 3.0%,
or from 2.0% to 2.5%.
[0103] According to embodiments, at a load of 10000 psi, the coated
proppant particle has a fine production from 0.5% to 5.0%, such as
from 1.0% to 5.0%, from 1.5% to 5.0%, from 2.0% to 5.0%, from 2.5%
to 5.0%, from 3.0% to 5.0%, from 3.5% to 5.0%, from 4.0% to 5.0%,
from 4.5% to 5.0%, from 0.5% to 4.5%, from 1.0% to 4.5%, from 1.5%
to 4.5%, from 2.0% to 4.5%, from 2.5% to 4.5%, from 3.0% to 4.5%,
from 3.5% to 4.5%, from 4.0% to 4.5%, from 0.5% to 4.0%, from 1.0%
to 4.0%, from 1.5% to 4.0%, from 2.0% to 4.0%, from 2.5% to 4.0%,
from 3.0% to 4.0%, from 3.5% to 4.0%, from 0.5% to 3.5%, from 1.0%
to 3.5%, from 1.5% to 3.5%, from 2.0% to 3.5%, from 2.5% to 3.5%,
from 3.0% to 3.5%, from 0.5% to 3.0%, from 1.0% to 3.0%, from 1.5%
to 3.0%, from 2.0% to 3.0%, from 2.5% to 3.0%, from 0.5% to 2.5%,
from 1.0% to 2.5%, from 1.5% to 2.5%, from 2.0% to 2.5%, from 0.5%
to 2.0%, from 1.0% to 2.0%, from 1.5% to 2.0%, from 0.5% to 1.5%,
from 1.0% to 1.5%, or from 0.5% to 1.0%.
[0104] According to embodiments, at a load of 8000 psi, the coated
proppant particle has a fine production from 0.5% to 2.0%, such as
from 1.0% to 2.0%, from 1.5% to 2.0%, from 0.5% to 1.5%, from 1.0%
to 1.5%, or from 0.5% to 1.0%.
[0105] The low fine production for coated proppant particles as
previously disclosed and described may be related to the increase
in hardness and elastic modulus provided by using the cross-linking
agent. Without being bound by any particular theory, it is believe
that when the cross-linking agent concentration in the co-polymer
matrix is increased, the hardness and elastic moduli are also
increased, as will be discussed subsequently in more detail.
Therefore, the enhancements in the nanomechanical characteristics
may be due to the formation of 3D-crosslinked porous networks. In
addition, the cross-linking agent crosslinking with the copolymer
matrix may further enhance the thermal properties like glass
transition temperatures (Tg) and degradation temperatures (Tdeg).
It has been found that the addition of cross-linking agent
increased the Tg of the copolymer. This shows that the newly formed
3D-crosslinked terpolymer network through cross-linking agent
linkages, was able to hinder the chain mobility of the terpolymer
matrix, thus requiring higher temperature in order for the polymer
chain to move freely. Consequently, increasing the concentration of
the cross-linking agent resulted in the subsequent increase of the
Tg. This may be credited to the increased crosslinking density of
the terpolymer matrix that was induced by the presence of the
cross-linking agent. In addition, further increase in cross-linking
agent concentration can lead to change in the overall chemical
composition of the polymer, such as the cross-linking agent being
incorporated into the copolymer backbone and creating a terpolymer,
thus increasing the Tg.
[0106] Nanoindentation measurements (hardness and elastic modulus)
are performed using a calibrated NanoTest.TM. system (manufactured
by Micro Materials, UK) with a standard diamond Berkovich indenter.
For each indentation cycle, the loading and unloading lasts 10
seconds (s), respectively, and the dwell time at each peak load is
5 s. Five measurements are performed on each specimen at the 0.1 mN
(or 100 .mu.N) load. The force-displacement (P-h profile) data is
used to evaluate the hardness (H) and the reduced elastic modulus
(Er). The elastic modulus (Ei) and Poisson ratio (vi) of the
diamond indenter was taken as 1140 GPa and 0.07, whereas the
Poisson ratio (vs) of the specimen was taken as 0.33 (considering
the vs as 0.33 for PMMA for the calculations of the elastic modulus
(Es). In preparation for the nanoindentation test, the polymer
samples is mounted onto the substrate base (steel disc) using
cyanoacrylate adhesive (superglue). Nanoindentation tests on all
specimens are conducted in air at room temperature (23.degree. C.)
in a temperature-controlled environment.
[0107] The elastic modulus (E) of coated proppant particles as
previously disclosed and described as measured by Nanoindentation
is, according to one or more embodiments, from 4.0 GPa to 7.0 GPa,
such as from 4.5 GPa to 7.0 GPa, from 5.0 GPa to 7.0 GPa, from 5.5
GPa to 7.0 GPa, from 6.0 GPa to 7.0 GPa, from 6.5 GPa to 7.0 GPa,
from 4.0 GPa to 6.5 GPa, from 4.5 GPa to 6.5 GPa, from 5.0 GPa to
6.5 GPa, from 5.5 GPa to 6.5 GPa, from 6.0 GPa to 6.5 GPa, from 4.0
GPa to 6.0 GPa, from 4.5 GPa to 6.0 GPa, from 5.0 GPa to 6.0 GPa,
from 5.5 GPa to 6.0 GPa, from 4.0 GPa to 5.5 GPa, from 4.5 GPa to
5.5 GPa, from 5.0 GPa to 5.5 GPa, from 4.0 GPa to 5.0 GPa, from 4.5
GPa to 5.0 GPa, or from 4.0 GPa to 4.5 GPa.
[0108] The hardness (H) of coated proppant particles as previously
disclosed and described as measured by Nanoindentation is,
according to one or more embodiments, from 0.10 GPa to 0.40 GPa,
such as from 0.15 GPa to 0.40 GPa, from 0.20 GPa to 0.40 GPa, from
0.25 GPa to 0.40 GPa, from 0.30 GPa to 0.40 GPa, from 0.35 GPa to
0.40 GPa, from 0.10 GPa to 0.35 GPa, from 0.15 GPa to 0.35 GPa,
from 0.20 GPa to 0.35 GPa, from 0.25 GPa to 0.35 GPa, from 0.30 GPa
to 0.35 GPa, from 0.10 GPa to 0.30 GPa, from 0.15 GPa to 0.30 GPa,
from 0.20 GPa to 0.30 GPa, from 0.25 GPa to 0.30 GPa, from 0.10 GPa
to 0.25 GPa, from 0.15 GPa to 0.25 GPa, from 0.20 GPa to 0.25 GPa,
from 0.10 GPa to 0.20 GPa, from 0.15 GPa to 0.20 GPa, or from 0.10
GPa to 0.15 GPa.
[0109] The ratio of hardness to elastic modulus (i.e., H/E) of
coated proppant particles as previously disclosed and described as
measured by Nanoindentation is, according to one or more
embodiments, from 0.040 to 0.050, such as from 0.042 to 0.050, from
0.045 to 0.050, from 0.470 to 0.050, from 0.040 to 0.047, from
0.042 to 0.047, from 0.045 to 0.047, from 0.040 to 0.045, from
0.042 to 0.045, or from 0.040 to 0.042.
[0110] The thermal stability of coated proppant particles as
previously disclosed and described in respect to the
functionalization of the proppant particles with the nanocomposites
is studied using thermogravimetric analyses (TGA) Hitachi STA7200
thermal analysis system. TGA of the prepared coated proppant
particles are recorded from 30.degree. C. to 500.degree. C. at a
heating rate of 2.degree. C./min under nitrogen flow of 50 ml/min.
Differential scanning calorimetry (DSC) was performed on a Hitachi
DSC7020. The samples were heated from 30.degree. C. to 350.degree.
C. at the rate of 5.degree. C./min under nitrogen flow of 50
ml/min.
[0111] The degradation temperature (Tdeg) of coated proppant
particles as previously disclosed and described as measured by
thermal stability is, according to one or more embodiments, from
400.degree. C. to 420.degree. C., such as from 402.degree. C. to
420.degree. C., from 405.degree. C. to 420.degree. C., from
407.degree. C. to 420.degree. C., from 410.degree. C. to
420.degree. C., from 412.degree. C. to 420.degree. C., from
415.degree. C. to 420.degree. C., from 417.degree. C. to
420.degree. C., from 400.degree. C. to 417.degree. C., from
402.degree. C. to 417.degree. C., from 405.degree. C. to
417.degree. C., from 407.degree. C. to 417.degree. C., from
410.degree. C. to 417.degree. C., from 412.degree. C. to
417.degree. C., from 415.degree. C. to 417.degree. C., from
400.degree. C. to 415.degree. C., from 402.degree. C. to
415.degree. C., from 405.degree. C. to 415.degree. C., from
407.degree. C. to 415.degree. C., from 410.degree. C. to
415.degree. C., from 412.degree. C. to 415.degree. C., from
400.degree. C. to 412.degree. C., from 402.degree. C. to
412.degree. C., from 405.degree. C. to 412.degree. C., from
407.degree. C. to 412.degree. C., from 410.degree. C. to
412.degree. C., from 400.degree. C. to 410.degree. C., from
402.degree. C. to 410.degree. C., from 405.degree. C. to
410.degree. C., from 407.degree. C. to 410.degree. C., from
400.degree. C. to 407.degree. C., from 402.degree. C. to
407.degree. C., from 405.degree. C. to 407.degree. C., from
400.degree. C. to 405.degree. C., from 402.degree. C. to
405.degree. C., or from 400.degree. C. to 402.degree. C.
[0112] The glass transition temperature (Tg) of coated proppant
particles as previously disclosed and described as measured by
thermal stability is, according to one or more embodiments, from
80.degree. C. to 90.degree. C., such as from 81.degree. C. to
90.degree. C., from 82.degree. C. to 90.degree. C., from 83.degree.
C. to 90.degree. C., from 84.degree. C. to 90.degree. C., from
85.degree. C. to 90.degree. C., from 86.degree. C. to 90.degree.
C., from 87.degree. C. to 90.degree. C., from 88.degree. C. to
90.degree. C., from 89.degree. C. to 90.degree. C., from 80.degree.
C. to 89.degree. C., from 81.degree. C. to 89.degree. C., from
82.degree. C. to 89.degree. C., from 83.degree. C. to 89.degree.
C., from 84.degree. C. to 89.degree. C., from 85.degree. C. to
89.degree. C., from 86.degree. C. to 89.degree. C., from 87.degree.
C. to 89.degree. C., from 88.degree. C. to 89.degree. C., from
80.degree. C. to 88.degree. C., from 81.degree. C. to 88.degree.
C., from 82.degree. C. to 88.degree. C., from 83.degree. C. to
88.degree. C., from 84.degree. C. to 88.degree. C., from 85.degree.
C. to 88.degree. C., from 86.degree. C. to 88.degree. C., from
87.degree. C. to 88.degree. C., from 80.degree. C. to 87.degree.
C., from 81.degree. C. to 87.degree. C., from 82.degree. C. to
87.degree. C., from 83.degree. C. to 87.degree. C., from 84.degree.
C. to 87.degree. C., from 85.degree. C. to 87.degree. C., from
86.degree. C. to 87.degree. C., from 80.degree. C. to 86.degree.
C., from 81.degree. C. to 86.degree. C., from 82.degree. C. to
86.degree. C., from 83.degree. C. to 86.degree. C., from 84.degree.
C. to 86.degree. C., from 85.degree. C. to 86.degree. C., from
80.degree. C. to 85.degree. C., from 81.degree. C. to 85.degree.
C., from 82.degree. C. to 85.degree. C., from 83.degree. C. to
85.degree. C., from 84.degree. C. to 85.degree. C., from 80.degree.
C. to 84.degree. C., from 81.degree. C. to 84.degree. C., from
82.degree. C. to 84.degree. C., from 83.degree. C. to 84.degree.
C., from 80.degree. C. to 83.degree. C., from 81.degree. C. to
83.degree. C., from 82.degree. C. to 83.degree. C., from 80.degree.
C. to 82.degree. C., from 81.degree. C. to 82.degree. C., or from
80.degree. C. to 81.degree. C.
[0113] The optical microscope (SCO Tech) was used to visualize the
coated proppant particle image at the micrometer scale. This is
done to compare potential morphological and shape changes among the
proppant particles. The samples are viewed at 40.times.
magnification for the objective lens.
[0114] The spherecity of coated proppant particles as previously
disclosed and described as measured by thermal stability is,
according to one or more embodiments, from 0.4 to 1.0, such as from
0.5 to 1.0, from 0.6 to 1.0, from 0.7 to 1.0, from 0.8 to 1.0, from
0.9 to 1.0, from 0.4 to 0.9, from 0.5 to 0.9, from 0.6 to 0.9, from
0.7 to 0.9, from 0.8 to 0.9, from 0.4 to 0.8, from 0.5 to 0.8, from
0.6 to 0.8, from 0.7 to 0.8, from 0.4 to 0.7, from 0.5 to 0.7, from
0.6 to 0.7, from 0.4 to 0.6, from 0.5 to 0.6, or from 0.4 to 0.5.
Sphericity measures the degree to which a particle approaches a
spherical shape. Spherecity was defined by Wadell, H., Volume,
Shape, and Roundness of Rock Particles, Journal of Geology, 1932,
40, 443-45 as the ratio between the diameter of a sphere with the
same volume as the particle and the diameter of the circumscribed
sphere. As used herein, the sphericity of a particle is determined
by measuring the three linear dimensions of the particle (longest
(L), intermediate (I) and shortest (S). The roundness of the
particle by visual comparison with the roundness chart. The long
(L), intermediate (I) and short (S) diameters of particle were
measured using calipers. From this, the ratios I/L and S/I can be
determine the sphericity (to the nearest 0.1 unit) using the Zingg
diagram, such as the diagrams in Zingg, T., Beitrag zur
Schotteranalyse: Schweiz. Min. Pet. Mittl, 1935, 15, 39-140, and
Aschenbenner, B. C., A New Method of Expressing Sphericity, Journal
of Sedimentary Petrology, 1956, 26, 15-31.
EXAMPLES
[0115] The following examples illustrate features of the present
disclosure but are not intended to limit the scope of the
disclosure.
Example 1
[0116] A 3D-cross-linked polystyrene-polymethyl
methacrylate/divinyl benzene (PS-PMMA/DVB) terpolymer intermediate
layer was formed on the surface of sand (i.e., proppant particle)
as follows.
[0117] Five (5) wt. % of AIBN was dissolved in acetone and added to
sand. The mixture of AIBN and sand was treated for 12 hours at
40.degree. C. to modify the surface of the sand. This step ensured
the presence of initiator (i.e., AIBN) at the surface of the sand
so that the polymerization will be initiated at the surface of the
sand once the combination of monomers were added to the sand. The
AIBN coated sand is subsequently referred to as surface treated
sand. Separate from the surface treated sand, the combination of
monomers was prepared by mixing 45 wt. % styrene and 45 wt. %
methyl methacrylate. Then 10 wt. % of divinyl benzene (i.e.,
cross-linking agent) was added to the mixture and sonicated for 15
minutes. Subsequently, 5 wt. % of recrystallized AIBN (i.e.,
initiator) was added as a super addition to the combination of
styrene, methyl methacrylate, and divinyl benzene. The mixture of
styrene, methyl methacrylate, and divinyl benzene formed a monomers
solution.
[0118] The monomers solution was added to the surface treated sand
and mixed with a blender. Subsequently, the mixture of surface
treated sand and monomers solution was polymerized at 70.degree. C.
for 1 to 2 days.
[0119] After the polymerization was complete, a curable epoxy resin
was prepared by mixing 80 wt. % bisphenol A epoxy resin and 20 wt.
% of an aliphatic amine curing agent. To this mixture, 0.1 wt. % of
XGnP-M-25 graphene Nanoplatelets manufactured by XG Sciences was
added as a super addition.
[0120] The curable epoxy resin mixture was added to cross-linked
terpolymer coated sand, mixed well with a blender, and cured at a
temperature of 150.degree. C. for 5 minutes.
Examples 2 and 3
[0121] The previously disclosed process was repeated to make two
additional coated proppant materials. However, in Example 2 the
amount of the cross-linking agent (DVB) was decreased to 5 wt. %,
and in Example 3 the amount of the cross-linking agent (DVB) was
decreased to 1 wt. %.
Comparative Example 1
[0122] The previously disclosed process was repeated to make a
comparative coated proppant material. However, in Comparative
Example 1 no cross-linking agent (DVB) was added to the combination
of monomers. Accordingly, in the coated proppant of Comparative
Example 1, the intermediate layer is a copolymer (i.e., not a
terpolymer) of polystyrene and polymethyl methacrylate (PS-PMMA).
For the purpose of clarity, the epoxy resin layer of Comparative
Example 1 is the same as the epoxy resin layer in Examples 1-3.
[0123] Crush Test
[0124] To show the properties of the coated proppant according to
embodiments previously disclosed and described, a crush test--as
previously described--was performed on neat sand (i.e., sand
without any coating), the coated proppant of Comparative Example 1,
and the coated proppant of Example 1 as follows.
[0125] The crush test--as previously described--was performed at a
load of 10000 psi. The neat sand produced 48% fine, the coated
proppant of Comparative Example 1 produced a fine production of
12.3%, and the coated proppant of Example 1 produced a fine
production of 2.09%, as shown in FIG. 3.
[0126] Without being bound to any particular theory, it is believed
that the decreased fine production for the coated proppant of
Example 1 at high stresses of 10000 psi is correlated to
cross-linking agent (DVB) in the PS-PMMA polymer matrix of the
coated proppant of Example 1 and the 3D-cross-linked terpolymer
network structures formed thereby.
[0127] A more detailed analysis of the fine production of the
coated proppant of Example 1 is provided in FIG. 4 where the crush
test was performed at loads from 3000 psi to 12500 psi. As shown in
FIG. 4, the fine production increases with an increase in the
applied load, and the fine production only reached a value of
approximately 5% at an enormous applied stress of 12500 psi. This
shows that the coated proppants of Example 1 have increased crush
strength and may be beneficial for use in deep subsurface
formations. As previously disclosed, any fine production less than
10% at an applied load of 10000 psi indicates that a proppant may
be suitable for some uses. The coated proppant of Example 1
significantly exceeds this standard, and shows its usefulness under
extremely high pressures.
[0128] Nanoindentation Test
[0129] The mechanical properties (such as elastic modulus (E) and
hardness (H)) were measured on the coated proppants of Comparative
Example 1 and Examples 1-3 using the Nanoindentation test as
previously described. Table 1 that follows shows the results of
those tests.
TABLE-US-00001 TABLE 1 Nano-indentation E (GPa) H (GPa) H/E Comp.
Ex. 1 3.82 0.130 0.034 Ex. 3 4.42 0.190 0.043 Ex. 2 5.40 0.240
0.044 Ex. 1 6.27 0.298 0.048
[0130] As shown by the above data, the high stress resistance for
the coated proppants of Examples 1-3 is further supported by
increased hardness and elastic modulus with introduction and
increasing of the cross-linking agent (DVB) in PS-PMMA copolymer
films. Also, as shown in Table 1, when the cross-linking agent
(DVB) concentration in in the polymer matrix is increased from 1
wt. % (i.e., Example 3) to 10 wt. % (i.e., Example 1), the hardness
and elastic moduli are increased from 0.190 GPa to 0.298 GPa and
4.42 GPa to 6.27 GPa, respectively. Thus, the H/E of the coated
proppants of Examples 1-3 also increased from 0.034 to 0.043 as the
amount of cross-linking agent in the coated proppant increased.
This enhancement in mechanical properties could be attributed to
the strong bond created as a result of DVB crosslinking. This is
significantly higher than the hardness and elastic modulus of
Comparative Example 1, which does not include a cross-linking
agent, and has a hardness and elastic modulus of 0.13 GPa and 3.82
GPa, respectively. Therefore, without being bound by any particular
theory, the improvements in the nanomechanical characteristics can
be due to the formation of 3D-cross-linked terpolymer porous
networks that are formed by the inclusion of a cross-linking
agent.
[0131] Thermal Analysis
[0132] Thermal analysis (such as the degradation temperature (Tdeg)
and glass transition temperature (Tg)) were measured on the coated
proppants of Comparative Example 1 and Examples 1-3 using the
thermal analysis as previously disclosed. Table 2 that follows
shows the results of those tests.
TABLE-US-00002 TABLE 2 DSC TGA T.sub.g (.degree. C.) T.sub.deg
(.degree. C.) Comp. Ex. 1 84.2 395 Ex. 3 86.7 403 Ex. 2 87.2 406
Ex. 1 88.0 411
[0133] FIG. 5 depicts the differential scanning calorimetry (DSC)
thermograms of the 3D-cross-linked PS-PMMA/DVB terpolymer of the
coated proppant of Examples 1-3 in comparison to PS-PMMA copolymer
of the coated proppant of Comparative Example 1. From these DSC
results, it was shown that the glass Tg of the coated proppants of
Examples 1-3 were 86.7.degree. C. (Example 3), 87.2.degree. C.
(Example 2), and 88.0.degree. C. (Example 1). By comparison, the Tg
of the coated proppant of Comparative Example 1 was recorded at
84.2.degree. C.
[0134] From this data, it is evident that addition of the
cross-linking agent (DVB) increased the glass transition
temperature of the polymer. Without being bound by any particular
theory, it is believed that this shows that the 3D-cross-linked
PS-PMMA/DVB network of the coated proppant of Examples 1-3 was able
to hinder the chain mobility of the PS-PMMA/DVB matrix, thus
requiring higher temperature in order for the polymer chain to move
freely. Consequently, increasing the concentration of the
cross-linking agent (DVB), resulted in the subsequent increase of
the Tg of the coated proppant. It is believed that this is due to
the increased crosslinking density of the PS-PMMA/DVB matrix that
was induced by the presence of the cross-linking agent (DVB). Also,
as shown by a comparison of Examples 1-3, it was shown that an
increase in cross-linking agent (DVB) concentration can lead to
change in the overall chemical composition of the polymer. Without
being bound by any particular theory, it is believed that the
cross-linking agent (DVB) was incorporated into the PS-PMMA/DVB
backbone and created a cross-linked terpolymer that increased the
Tg of the coated proppant.
[0135] In addition, the thermal stability of the coated proppant of
Examples 1-3 in comparison to the coated proppant of Comparative
Example 1 was studied using thermal gravimetric analysis (TGA) and
the results are shown in FIG. 6. From this figure, it was observed
that all the synthesised polymers in the coated proppants undergo
one-step degradation. The maximum weight loss was seen to take
place around 395.degree. C. due to the decomposition for the
PS-PMMA backbone. However, this temperature shifted to higher value
upon addition of a cross-linking agent (DVB). This reflects the
effect of a cross-linking agent in the PS-PMMA matrix, enhancing
its thermal stability. The Tdeg of the coated proppant of Examples
1-3 was increased with increase in DVB concentration.
[0136] Optical Test
[0137] FIGS. 7A-7C show the optical images of neat sand (FIG. 7A),
coated proppants of Comparative Example 1 (FIG. 7B), and the coated
proppant of Example 1 for analysis of roundness and sphericity.
From these figures, it is evident that the coated proppant of
Example 1 was observed to have the best sphericity, such as
roundness and sphericity of 0.6 or higher. As previously described,
the optical microscope (SCO Tech) was used to visualize the coated
proppants at the micrometer scale. This was done to compare
potential morphological and shape changes among the sand particles.
The samples were viewed at 40.times. magnification for the
objective lens.
[0138] FIGS. 8A-8C show SEM images of the coated proppant of
Example 1 at different magnifications to measure for roundness and
sphericity. FIG. 8A shows the coated proppants of Example 1 at
50.times. magnification, FIG. 8B shows the coated proppants of
Example 1 at 200.times. magnification, and FIG. 8C shows the coated
proppants of Example 1 at 500.times. magnification. It is evident
that the proppants related to current invention had excellent
roundness and sphericity.
[0139] It should be apparent to those skilled in the art that
various modifications and variations may be made to the embodiments
described within without departing from the spirit and scope of the
claimed subject matter. Thus, it is intended that the specification
cover the modifications and variations of the various embodiments
described within provided such modification and variations come
within the scope of the appended claims and their equivalents.
[0140] Having described the subject matter of the present
disclosure in detail and by reference to specific embodiments
thereof, it is noted that the various details disclosed within
should not be taken to imply that these details relate to elements
that are essential components of the various embodiments described
within, even in cases where a particular element is illustrated in
each of the drawings that accompany the present description.
Further, it should be apparent that modifications and variations
are possible without departing from the scope of the present
disclosure, including, but not limited to, embodiments defined in
the appended claims. More specifically, although some aspects of
the present disclosure are identified as particularly advantageous,
it is contemplated that the present disclosure is not necessarily
limited to these aspects.
* * * * *